to think starting a relationship with a parent is inappropriate?

Could be anything I am suggesting that it is useful to honestly look at your own intentions and motives before talking action (try to fast forward to the outcome of your actions
we only have ba snapshot of what the whole scenario only the OP knows the full dynamics

It would give me the ick, were they eyeing each other up when he was doing pick ups?

You need to draw a line when it comes to the house - it muddies the waters a little. It is now your home with your DC, he can be a guest when you are there but needs his own place for when he has the girls. You are now divorced and your only common denominator now should be the children.

I don't think legally she is doing anything wrong, but morals I would be questioning, especially messaging you about it and being in your home with him.

Yes this. I was ready to read you being ott, but I'd agree it's very fast to be introducing children into the situation - morally.

Professionally, it's nothing to do with it.

I think most men seem to think with their Dicks sadly.2 GF in a very short space of time is a lot.Introducing them to the children so early is not really on .However he isnt breaking any laws .I would have a chat and tell him you are unhappy with the arrangements . A clean break and 2 houses will be better I think .As far as School goes there are no rules on dating parents I dont think.A Teacher at my Sons school dated one of the Dads there .

Teachers are allowed to date parents as they are not vulnerable service users. But I think you should chat to your ex about Boundaries - there are no risks at all (just a little inconvenience for the adults) to waiting for the new partner to spend lots of time with the children, but there are many risks of rushing a step family unit too soon.
my ex moved in with a woman and her child that he’d only known for 6 months and had my toddler son for sleep overs there then (ive since found out) they broke up 6m later, they still lived together broken up and then she and her child moved out - my son had experienced all of these changes and he didn’t tell me what was happening. Both children must have been so upset and confused especially the ex gfs daughter who was older and lived there full time

I'd tell her she wasn't welcome in my house and he has abused that privilege and that arrangement was ending. It was too much for the girls and not convenient for you. What they do elsewhere is up to them and you don't care.

Nesting is supposed to be for the kids benefits, but really unless you are really good friends the stress it puts on the ex partners is going to cause so many problems when they try to move on with their lives.
I would run a mile before dating anyone in that situation.

I agree. Too many posters on MN are too quick to label people “jealous” when often they are actually disturbed/angry/worried/anxious/concerned.

I think setting boundaries about what is acceptable when Nesting is fair.

it’s really frustrating and I would feel the same, but just think, do you like the woman? The children seem to? If the answer to that is yes, and yes for the children.. then that’s an overall win because they will be around your Ex husbands partner.
the best you can hope for is consistency. If it doesn’t work out between them, then respectfully tell him he shouldn’t introduce these people to children until he’s sure about them.

I think you can explain the situation to your child's teacher, not with a view to the school doing anything but so that if things are awkward at school between the children and the preschool person there's an understanding of why that might be.

It would be more awkward if the preschool person didn't say hello/otherwise casually interact with the children at school.

But there's a whole host of stuff that might become a problem eg. calling her by her first name, mentioning her children to the other kids at school - I'm sure there will be teachers reading this who've had to navigate having their own kids in their school with them.

Can you create a separate bedroom space for your ex in your house so you can lock your own when you leave? I'm not sure you're going to find good alternatives to swapping adults in that house unless one of you has a vastly improved financial position.

If his problem is wanting someone to help him do his parenting you could consider suggesting friends you're happy having in your house +/- his parents/siblings. He doesn't have to start a romantic relationship to get childcare support.

I agree and am.amazed by the number of people who think it's ok & not a concern

I imagine the school staff all know what's going on but maybe the senior management don't know the details.
If the nursery school is part of the primary it may well be against the school code of conduct but perhaps the teacher isn't that daft

This. I actually think it's very confusing for the children to have dad in their home with another lady. Especially their teacher...
He needs to find another way to have them, airbnb or whatever. It's just too mixed up.

I'm glad you've realised the "nesting" arrangement has to end. That's one of those great-seeming ideas I've never seen work out positively in real life outside of the initial weeks after a separation. I know it sounds so kind for the kids in theory, but in practicality it always seems to create more toxicity in the parent relationship and prolong the most painful part of transitioning to two households.

I think your ex and the new gf are wrong to introduce any sort of relationship to their children this quickly (saying "she's a friend" to young children makes zero difference to young children). You should tell your ex your concerns but realistically you can't control how he introduces new people. Tell him the nesting arrangement will end on X date, don't attach any conditions relating to relationships to it.

But this isn't a school matter. The only way that would change is if there was specific behavior at school that was inappropriate - and saying hi absolutely doesn't count. If this teacher behaves in outwardly hostile ways towards you or your child, uses her staff position to interfere in your DDs education or access information she has no professional reason to have then that's different. And of course if she ever moved to a position where she was directly responsible for your children that would be reason to object.

I’m absolutely baffled by this. Entirely agree that she shouldn’t be spending time with DDs, imo opinion you should wait to see how things progress before introducing a new partner, but everyone’s different. My problem here is that she’s in a professional role relating to your DDs and is now seeing one of the parents. I used to work in schools and if that had ever happened management would have been horrified. It’s a line you just don’t cross, especially given the kids were in her class literally a few months ago. So so so many safeguarding implications around this (how would she react if the children made a disclosure given she’s now personally involved with the family?!). She also shouldn’t be messaging you. If I ever had to communicate with any parents it was purely on a professional level and done through email/school phone etc. I’d be telling management about this straight away. She is incredibly naive if she thinks this is okay and acceptable

Like others, I also think your ex is only interested in his needs. I suppose he thinks that the children will all play together and occupy each other while he and their mother get to know each other. Your children will already be trying to process that you and their father are no longer together and it will hurt them and confuse them to see him being intimate with somebody else no matter who it is. The teacher really ought to have more sense. I can’t see this relationship lasting that long because I don’t think they’re on the same page. It sounds like she is looking at him as a long term relationship already, asking you permission etc and gushing so much. I think she’s going to get hurt too. It seems to be a pattern with newly divorced and separated men to try and shag as many available women as possible without a second thought.

Imo, very unprofessional and unacceptable. Inconsiderate of your ex. I would consider speaking to the school.

I would assume she wants to protect her children and their happiness & prevent their confusion rather than it being "jealousy"

What are your motives here
are you wanting to get a situation of harmony or are you trying to sabotage the new relationship ?
maybe if you look at your own intentions- are you jealous it would be perfectly natural to feel sidelined
do you want to control the outcome .?

‘Nesting’ is the issue here - you need to get out of each others lives more.

While I understand this is upsetting for you, I don’t think they’ve done anything wrong. Two adults entering into a consensual relationship. The play date seems fine given the usual wait is usually about introducing a stranger into children’s lives - this could genuinely be passed off as a play date. If you report this to management, you’ll come across as extremely petty.

They’re both saying that the usual 6 months don’t apply because she already knows the girls. But this isn’t the point, as I understand it, waiting isn’t just to suss out if the new person is ok, it’s to see what’s going to happen with the relationship before the children get attached and then disappointed.

There's no "usual 6 months".

How would you ever prove that?

Surely she’d say she got it from the children’s dad…

How old are they?

I don’t think it’s ideal, but I don’t actually think it’s wrong. On the plus side you know this woman is a decent person to have around your children. Although I understand why you would be hurt, I’d try and look at this objectively.

In terms of telling her employer, I don't think you will need to - I would imagine they already know, primary schools are relatively small places & gossip travels fast.

As others have said, she & your exH probably waited until your children moved on from the nursery so technically she has done nothing wrong but I would be surprised if the senior management of the nursery and school don't share most posters view of this situation.