SIL uninvited DCs to party

[Cocoadoodle]

SIL is having a big birthday party tomorrow night. It’s family and friends and has been booked for ages at a local venue with bar, disco.
Family are coming from different parts of the country, with some staying at other local family members homes and some staying in hotels.
We have 2 DCs, so SILs niece and nephew. DD 10, DS 7
This morning she’s nonchalantly messaged me saying oh no, just found out after speaking to the venue that kids aren’t allowed. I asked her weeks ago and she said they were! My DC are so excited to celebrate their aunts birthday and see their cousins/other kids from extended family, and now they can’t go and she doesn’t seem to give two shits! They’re going to be gutted.
Cousin (in law) is driving over after school tonight to stay at ours with her kids for the weekend, and SIL hasn’t even bothered to tell them that their kids are now not invited.
I know I’m not being U, but what are we supposed to do? Or maybe I am being U as it’s her party so she can do as she pleases.

People are traveling in from out of town. They don’t have trusted babysitters.

Well she's not wrong she is dense for not checking before booking. It's just basic common sense birthday that if you know children will be there you check they can go. Not just assume they can.

It's annoying and inconvenient, but not the end of the world. The family can either let this be a funny story that the SIL never lives down or let it cause ongoing grudges and major family rifts.

Frankly? I'd not go. And if i were one of the ones driving in? I'd not bother.
And if SIL said anything i'd say "oops - forgot to tell you" and leave it at that

Surely everyone grasps that they need looking after though?

I was trying to put myself in SILs shoes to see how I'd feel if a load of guests now said "soz, that's a no can do from us" and they don't travel over to stay with other family.

And I'd be upset that they weren't coming, with such short notice. Then I'd go and enjoy my party. Because, obvs, the SIL has the attention span of a goldfish so it will upset her for about 20 seconds.

or something.

I'd have a night in with the kids watching films and eating pizza. And DH would be free to decide what he did.

Tell hubby he can go but I wouldn't go now. Let the kids dress up with their cousins. Take them out for food and let them have ice cream and watch Christmas movies. Your SIL. Is a ninny!

NTA
I'd call the venue and verify if kids can't come. Then proceed from there.
If venue says kids can come I wouldn't tell her but would let others who were told no that kids are welcome at venue others and bring the kids.
If they can't well I'd set up an alternate meeting spot for everyone with kids: Chuck E Cheese, Pizza Ranch whatever and just skip out on her event with an oh I thought I told you we couldn't get a sitter.

Any update, OP? Presume the party is due to start soon , without all the families...

So what happened ?

Just don't go. Any of you.

I’d be uninviting her from Christmas tbf

@Cocoadoodle - any update OP?

Cupid Stunt.

I’d suggest you and your cousin-in-law take your kids out somewhere special and have a good time. Don’t bother going to the party!

Disappointing but don’t go.

I’d ring the venue
I think she fibbing.

I once invited all my family members to my wedding but totally forgot a cousin who I never see. I’m dyslexic and was totally overwhelmed by the organising - it was a genuine oversight. I think it’s easy to jump on the bandwagon and say how awful she is but people can sometimes make assumptions and damning mistakes. How about rallying round to help her out? She must be really embarrassed and worried about spoiling everyone’s night. It’s her birthday and she’s made a public boo boo. If you’re good friends/family, forgive her 🙏🏻❤️

I'm so glad I don't have family, dreadful or otherwise, to consider. I'd want to wring their necks.

The OP says she has (12.24 yesterday). She’s not.

You are being unreasonable.
she hasn’t uninvited them she’s just realised they aren’t allowed at the venue.
get all the cousins together at a house and get a sitter.
I swear some people just choose to be offended

I think she is going to be very disappointed when everyone with kids pull out. Her fault, her loss.

your SIL has totally fucked up here. This will mess so many people up, as a result she will now have far fewer people at her party. Hope you and the children have a nice night regardless.

Sorry just really quick update and hopefully have more time tomorrow to reply more thoroughly.
Cousin-in-law and family now not staying at ours as they decided not to bother driving over for a party they can now not attend.
DC and I are going to my mums with cousins from my side of the family (costumes and all) for music, games and takeaway. DH is going to his sisters party even though he’s mightily pissed off with her.
Thanks for everyone’s replies and I will aim to respond tonorrow.

I thought it was just me who was puzzled at the number of people who purposely misrepresented what OP said! (I'm from the US and had thoughts of "where the heck did that come from").