I have nothing against involved SPs, and I give a lot of grace to SPs who overstep because they are overzealous, didn't know, were new, etc. However, once an active parent says "hey, back off", the SP needs to back off.

As much as I hate the BM in my life and think she's a worthless parent, her word trumps mine (okay, maybe less now that she has abandoned her parenting duties, but that's a separate thing). And I have swallowed my pride and bit my tongue more than once to enforce something with the boys that she has asked of them.

Very liberally use the word "no" with her when you're around. When you're not there, if she wants to look like an idiot, let her. But you wouldn't be wrong to tell her to take several seats and participate like a grandparent or aunt - from the sidelines, cheering the kids on. If it becomes a situation where PAS is happening, I highly recommend an updated - and strictly followed - CO.

I get wanting her to back off... but she's giving him food and hugs.. what are so threatened about??

Would you rather she ignore the kid altogether? Not give him snacks? Not make him feel loved by his father's wife?

Again.. I get wanting her to back off... but from What, exactly?

Honestly, she will probably burnout and settle down fairly soon. She's probably going over the top because she wants the kids to like her. It's normal. She might bug your ex to be more involved. 
Most likely though she will run out of enthusiasm before long and back off. try to be patient. Changes in life are not easy for anyone, especially kids, so your  patience will benefit them.

I think this falls under the category of things you can't control - she's not harming the kids. Most likely the coaches will eventually tell her to back off.  Don't be the insecure ex, this will blow over.

I think that this is a problem for the  coaches and league officials to solve.  Make anonymous complaints about parents entering the playing field.  Eventually, a coach or official will take care of it.

My mom brought me KoolAid powder, etc... to my elementary school field day when I was in 5th grade and I was asked to tell her that she could not do that since not all of the kids had the same thing.  It only happened once and I remember that incident from 45+ years ago like it was yesterday.  I told the teacher who approached me on it to speak to my mom if she had a problem with what my mom was doing. I did speak with my mom that eventing and asked her not to bring stuff to the next field day.

Once the coaches or officials speak to her about it they also need to give all of the kids the same message about keeping their parents in their places in the stands or on the side lines.  A mortified kid will move mountains to keep an overstepping parent in line.  Including a SParent.

When I used to officiate my SS's little league I did eject a PITA father once.  We had LEOs at every game.  They actually walked him to his car where he sat for the rest of the day.  The league did ask me in to discuss the incident and recommended that I be a bit more tolerant with the parents.  I told them that if I felt a parent was interfering in the game that I would do it again.   I only had to do it once.  

I can see you frustration in this situation. I would attend events with SO only to support him because he didn't want to have to interact with BM.

I was not there to take the place of BM or act like ai was a parent. 

From what you described it sounds like exH and new fiance are behaving as if they are trying to push you out.

I would just ignore them and not let it get to you. Fiance trying to make an impression on your kids and exH will wear off.

She's trying to play MOTY to win brownie points from all the other adults around. She probably feeds off the attention. Bet her makeup was perfect too (lol).

I can see your frustrations with sports signing up and etc. I attend more sports game when I came in the picture then BM and SO. I wasn't running on the fields etc. I'm not that person in general. I was there to support kids. 
 

BUT... not a single "mom" every attempted to talk to me. Make me feel welcome etc. I would be at some games alone and no one would interact with me. They knew SO or BM (everyone I think knew who BM was a POS then) but, it made me feel almost unwelcome. I had some dads talk to me but, once again not a single mom. I saw it as typical female jealously to be honest. (I was younger then most of them by probably 5-10 years) I'm not having kids at this point in my life but, If I did and saw a "me" in the crowd.. I'd make her feel welcome. 

We live in a typical nicer middle class town and everyone is clicky.. just like high school. 
 

Now... not once did I try replacing BM. Not once have a filled at a single form for skids.. which have been with us full time now for over 3 years. Prior BM was EOWE. SO always took care of everything. 
 

I'm going to be honest the ****MY**** kids triggered me. When BM and I had our blowout via text she did that same thing to me. Everything was MY!!! KIDSSSSSS!! Like I said, never tried replacing her was only being supportive and giving the skids a fulfilled life. 
 

I think let the games thing go for now. The skittles thing is annoying I get it. The coaches will probably be a stop to it. As for the actually signing stuff up.. I'd have a convo with your ex to just communicate with you better about this so you can line up schedules correctly. 

You can hope for the bilingual karma bus to come and run them over.

I was hit by it when I was in my 20's.  A friend and I were on public transport and started talking about a guy sitting opposite us in our obscure official native language.  In reality most people speak English on a day to day basis and can hardly string two words together in the language we were using.  We were in a completely different country so had in our minds no chance of bumping into another native speaker. 

The guy chipped in after awhile in our official language to say thank you for the compliments.  Thank dawg we were only commenting on the fact that he was good looking.  I have never assumed that the people around me all couldn't understand since.

Hopefully, someone in amongst the parents, spectators, coaches will do the same thing to your ex and GF.  It will be worse for them because it sound like they are being d*cks

When exhusband and SM first got together (they met online and she moved from California to FLorida to be with him) my DD then 5 got really sick and was hospitalized for over a week with something called strep pneumo in the orbital socket and it was pretty serious and she could have lost her eye sight.  The symptoms first appeared on their day and SM took her to the ER and DD was admitted.  For some reason they gave her the parent badge.  I was 7 or 8 months pregnant with my now 6 year old at this time. The doctors would come in and speak to her as if she was the mom.  They would ask her if there were any allergies.  They would discuss treatment options with her.  I think its because since I was so heavy pregnant I had to sit in the chair in the room in the corner and she was always sitting in the bed with DD.  I had to constantly all the time interrupt and say , "I'm the mother!" And the tenth time she tried to agree to some treatment or speak on allergies (she'd only known them a few weeks at this time) I really came unglued in the hospital with the doctors and they ended up banning her and she could only come up with my permission.  

She also cut my DD's hair.  She had long straight hair and it was her first haircut and just off the plane from California she pretty much had it cut off to a pixie cut with no input or word from me.  It was her first haircut and I have no lock from her first haircut like I do from my other kids.

She took over and cut me out on the first day of school too.  My entire life all I've ever wanted to be is a mother.  I used to sit in my car as a young woman in my twenties stopped at the light and watch all the little kids with their backpacks and lunchboxes going to school  on the first day and dream of the day I got to experience that.  My exhusband  didn't even want kids and his wife  either doesn't or can't have kids but I desparately wanted to be a mother and I'm a good mother.  First day of school they show up and pick up younger DD (of my three with ex husband) and SM is literally carrying her the whole time and the teachers are assuming she's the mom and it just ruined it.

So we had to have a come to Jesus meeting. I really had to put it all out on the line to the both of them.  I said t"Do you want DD6's dad taking our oldest daughter to her driving test when she turns 16?  Do you want him taking her to the Father/Daughter dance? Somethings are for a parent to do and for a parent to experience.  I would never ever dream of taking my step kids prom dress shopping or wedding dress shopping if their mom wants to do that with them because it's a mom's role!!"   And pretty much after that come to Jesus meeting we've gotten things straight.  

If theyre putting on a show for a reaction just ignore them. As far as the activities, sign him up for what you want to sign him up for and do what you want to do with him.

Just don't be complaining about the SMs lack of involvement if she does back off and stop acting as enthusiastic.

You can't really control the situation or how your ex and his fiance are acting, but you can control how you react to it. Stop reacting, if your ex and his fiance really are just doing this for show they will get bored with it soon enough when you stop commenting. If they are legit their for the kids your lack of reaction won't really matter all that much.

When you split from exH did you ever sit down and discuss what expectations are if the other gets a new partner that will be around the kids? Most steps go in blind because nothing is ever communicated to us so if we over step it's like stepping on a landmine we weren't even aware was an issue.

Try and talk with your ex, if he's being HC try reaching out to his SO about boundaries. I do agree with you being upset about giving your kids sugary snack while doing sports. That's not good and will just slow them down if anything.

Chances are she is just trying to make a good impression and starting a little too strong. Your ex is probably egging her on, encouraging her to be "over the top." If he said he would find a new mother, he's probably putting her up to this and crossing all kinds of boundaries and pushing her to act more "motherly" than she feels comfortable being. She will probably burn out or realize the inappropriateness eventually. If she realizes it on her own, it will be a lot more effective in helping her set her own boundaries against what your ex is pushing her toward. If you make a fuss, you make yourself a convenient villain and it's evil BM (you) making their life hard. 

I truly believe most women dating a man with kids just want a relationship and don't have any desire to "steal" another woman's children. It's truly not the same and she will never replace you. You've read the stories here. If kids will blow off the hardest-working and best-meaning of stepmoms for a POS biomom who does the bare minimum, you have nothing to worry about. Really.