To cancel DD’s birthday party because I know her dad will ruin it?

The hall must be very small to only accommodate that number however I agree with your daughter, bringing the GF and her younger children is really not on, your ex-H must be devoid of any imagination if he can't see why that would upset his daughter.

He'll be thinking he can show off to his parents and girlfriend what a smashing dad he is (yeah just rocking up to a party he's not organised or paid for but happy to stand there and take some credit!)

He's likely already told the girlfriend it's all fine, so she's thinking woohoo free food and entertainment for my kids.

And that all matters more to him than how his daughter feels, and he'd rather dismiss how she feels. He says she'll be fine but what he really means is she'll just have get over it. On her birthday. What a knob.

Clearly didn't check or discuss the most basic thing for a party: who's coming. Date, arrangements for the rest of the day, yes. Read the OP and there's a lot of assuming going on. Probably on both sides tbh, looks like ex assumed OP would do the planning and he'd be there same as many not-ex husbands/fathers do...🙄.

The hall has a capacity. That's it. End of story. There's not space for everyone that he wants to bring. He can come, he can bring 1 other adult (same as you). He cannot bring extra people and they will be refused entry on the day due to the capacity limits

The word you need here OP is ‘no’. No, he can’t come, his parents can’t come and his girlfriend and her children can’t come. No. This is a party you are organising and paying for and he agreed to give you the time to do this. There isn’t an issue with him not being invited to the party you have organised and paid for, because obviously he can be at the one HE arranges for her, where his parents and girlfriend can also come and anyone else he and DD agree. You will not be at a party he organises either. Fair’s fair.
Tell your DD sorry but you can’t cancel because you have already paid for it. You can cancel if she insists, but there will be no alternative treat as the money was spent on the party. She is 10 she needs to learn that reality. Hopefully not a problem once you have told her dad ‘no’.
Going forwards, arrange things on your time only to avoid this. If that means DD needs a party organised on dad’s time, tell her to speak to her dad. There is nothing you can do as she will not be with you at that time. Then talk about what you will arrange during your time.

He's unreasonable to try and piggy back his entire family into the event to make it look like he's been part of organising something amazing for her. If his family genuinely want to see her for her birthday then he should arrange a similar thing or family meal etc.

That said, if it's his weekend then it's a bit messy, think it could have been communicated better on both sides.

The problem is, the divorce politics are all playing into this. If we remove that... any 10yo girl having a birthday party with friends likely wouldn't want grandparents et al tagging along. I'm amazed your ex can't see why this is inappropriate. Especially the gf's younger kids too.

I think you need to tell him straight- DD is getting too old to have the whole family tagging on to a party with her friends.

That won’t work, I presume he will just turn up anyway with his entourage, knowing that OP won’t be able to make him leave without causing a scene

I think you’ve learned a good lesson here about how to avoid this in future.

personality I’d say him and his parents can come if they really want to as it’s not really fair for you and your mum to host on his weekend. Then he can bring her back to his afterwards. The random tiny children aren’t invited, that’s not a thing - my kids have almost never even gone to each other’s parties as they’re for friends. In fact, I don’t think my husband has even been at the vast majority of the parties either - he usually keeps the other child home with him and I host on my own.

I understand why you booked it but I think having your mum there and it being in his weekend and him assuming every activity is a big family affair is confusing something that should be simple.

exactly. He sounds like an involved Dad. You sound controlling - and your daughter is parroting your behaviour / reaction. And yes I also Co parent.

It’s very hard OP and I disagree with what he is trying to do but perhaps in the future you need to be honest with your DD if she wants things on specific days that fall on her dads days. If you’d have had the party the weekend before/after this situation would be so much easier to avoid. She’s understandably upset now because what she was expecting isn’t happening, whereas if she’d have had this expectation managed from the start then I doubt she’d be so upset.

I think making the best of a tricky situation would be to allow Dad, GF and grandparents to come but I would draw the line at letting the GF’s younger kids come. They will change the dynamic and would do even if they were full siblings. It’s fine for your DD to have the day just with friends her own age.

I wouldn’t have thought it would matter about capacity with the adults so much? You might just have to tell them there will be nowhere to sit but they are welcome to come.

Just let them come and stand awkwardly on the sidelines.

If he must come, ignore him. Tell him you’re not able to cater for extra guests; no food or party bags. Let them stand about looking mardy.

I would make it clear this is a girls only birthday party as requested by your daughter. There is a strict number allowed in the hall, which can't accommodate additional people. He can if course arrange another birthday celebration after, to include his parents and other relatives. If he wants to upset his daughter's plans and create a bad atmosphere at her birthday party, that is on him.

Often in halls like that there are separate smaller rooms to the main space. Sometimes they have good outside space as well. If her dad's girlfriend's kids are going to come a space like that could be used to provide age appropriate entertainment for them.

Might work to invite a parent of a party child with a younger siblings to stay too and then the younger kids can entertain themselves with supervision whilst the party happens.

But really, I think the answer this time to your ex is 'no, the party has been paid for. It's a girls' party not for smaller kids and doesn't need or have space for extra adults. $daughter is spending these two hours with her friends. It's not a family party. We can plan next year differently but we're not changing what's been arranged for this year'

OP is not preventing him from being part of her birthday! there was a plan for him to have his daughter after the party and to take her out for cake, et cetera and a meal! however it’s a party that SHE has paid for. Why does HE get to go to it?

It's probably best not to involve your DD in the back and forth between you and ex. She's going to want to cancel and agree to a shopping trip to keep the peace.

The hall is obviously very small with the max number allowed so low. The only thing I would do is speak to him, tell him you need to be heard, say that your DD is now 10, more grown up, no baby parties anymore and this is what she wants. She wants just her friends and cousin there, say the hall won't allow extra people and if it did you would be happy for everyone to attend but it's not practical.

Tell him he has 2 options, let her enjoy her party with her friends that SHE wants as she is the most important person in this, he can collect her after and have his own family party with her doing anything he wants or they can all turn up but that they will probably not be able to stay as the hall will be at capacity and NO parent is staying.

Because it is her birthday

Your poor DD. Of course he can be there, he is her dad and she would love her GPs. I get that the girlfriend and her kids might be painful for you, but you could have made all this easier for your DD.

Poor OP, you are getting a lot of flack for trying to do right for your daughter. Ex AGREED ( how many times does this need to be said!) to the original plan and is now changing the narrative. Some posters agree with him , and another poster went as far as suggesting you provide separate entertainment for the GF kids!! Blood hell, she must be the GF.
As I see it the hire agreement is for 11 kids
1 entertainer and 2 adults (presently OP and her mum helping) That's 14.
Ex wants to add 6 . He could come to replace your Mum and actually be useful with a tea towel!
To cover your back, get this hairbrained gatecrash plan on text so you have evidence it wasn't your plan to shoehorn extras into the hall against the stipulated conditions of hire.
Good luck, OP, I hope your DD has a happy birthday despite all this shit.

This is BS lol. It’s obviously a kids party venue, just for children. No one has a kids party and invites all the family. Maybe if it was a big party in a large venue, but it’s obviously not.

Can you not just tell him your daughter wants to cancel it since it won’t be how she wants it, and that you’ll be taking her shopping instead. But then actually just have the party? It would be so much easier without him there

Just tell him no and be firm
You want to upset your daughter just to accommodate this whiny man
Do what you originally planned what your daughter originally wants and tell him to get stuffed

Birthday celebration is for 10 year old girl and it will include other 10 girls of same age. What’s the need for all the adults to arrive there plus unrelated two kids who are much younger and dd does not want them there.

Father is acting selfish. Op has organised what dd wanted. It’s not for op. Father should have checked with his dd what she wanted and organised her party with her friends. But since he didn’t do any organising, he should let dd enjoy her day. She can meet grandparents and whole army of relatives afterwords or next day.