How can I turn down uninvited siblings politely from nieces 9th birthday party?

Say they can attend at parents cost.

This.

How rude !!
“The numbers have been given in and I’m afraid we can’t accommodate any more children . I understand if this means little Jonnie can’t attend.

Please be polite but clear and direct. You can’t accommodate siblings

Great message.

this hits the spot

it's clear they have the choice too pay or not come and its polite

Perfect.
No ifs or buts, sorries or room for accomodating grasping parents.

I am sympathetic to the point about gossip concerning OP’s sister, but the woman has a nine year old DD and these are here friends. For that reason alone the point is likely moot.
And it will become clear at the venue that something is wrong. Leaving it to the imagination is not usually a good idea.

I think it is perfect that OP is the outsider that is now in charge:

Hi Mums,
As you know my DS suddenly became ill and req'd an operation. I'm stepping in essentially last minute to help out and plans have been set. Sorry, I'm not able to facilitate extra kids or other changes. Thanks for understanding.

This one. It's clear and tired the point.

I worry that 'you can come and pay' may end up with you being left in charge.

I think I a clear and absolute no is needed

"Ah its ok you can drop your child off, you dont need to stay I have another adult with me to look after the kids so you're free to care for Lucy/katy/whoever and pick up at xx time"

Or "its already booked but the website is www.whatever if you want to see if you can book <extra random child> in. For food we're going to the KFC nearby so again youre welcome to come along with <extra random child> and get them something. See you there!"

I'd reply no problem just drop Katy off to party and I will drop her home afterwards.

When it’s very young children, and the parent has to stay…sometimes older siblings need to be there as well due to no other childcare options. However, the parent should be providing for that other child in terms of food and things to keep them entertained (such as bringing a Nintendo to keep them occupied). They are not part of the ‘party’ and should be only the outskirts of it.

It sounds like these 2 mothers are just after some free childcare and free lunches for their other children, unless they are mistakenly thinking they need to stay for the event. The won’t have childcare for the other child routine is nonsense, because they are responsible for one less child when they drop one off at the party….so it reduces existing responsibility, not increases it! What they are really saying is that they don’t want to be bothered with driving their kids to a party and providing a birthday present…unless there is something to gain for the parent (an afternoon free of all childcare responsibilities).

Aside from the financial issue here, as it’s obvious that anyone not invited should be paying their way…you should also be considering the birthday child herself. Is she a child who really enjoys the company of kids of varying ages outside her friendship group? If the activity is bowling for example, having a 4 year old taking part could be disruptive to older kids who want to take it seriously. There’s also the risk with younger kids being spoilt brats who want to blow out the birthday cake candles or having tantrums wanting to be opening presents or opening party bags that are meant to be surprise contents at the end. With older children attending you have other potential problems, there is a risk that they will win any competitive activities and not give the younger kids a chance, meaning the birthday child doesn’t get a chance either, and there could even be issues like the older sibling is someone who is a bully at school and makes some of the younger kids feel uncomfortable. I think you need to ask the 9 year old whether she cares if siblings attend, if she doesn’t want that then it’s a straightforward no…even if that means a couple of her friends then don’t come. At age 9 she’s old enough to understand that it was cheeky of them to ask for free childcare and free meals/activities for kids who weren’t invited and be told it wasn’t their friend not wanting to come that caused the issue.

As it’s a one-off, I also wouldn’t worry about being rude or falling out with these other parents. Your sister can always do the “I was so ill I didn’t even know what my sister was doing during that week, I had no choice but to just let her take over, she doesn’t have her own kids or experience of any of this and just did her best” and just refresh whatever her relationships were with these other parents later.

Also…if this has happened AFTER you stating on WhatsApp that you are the Aunt taking over, they might be pushing their luck thinking you’ll be a soft touch.

@ThePetiteMermaid the first post nails it. Send that and hold firm if they try it on on the day.

So glad I'm past all that. Good luck.

"there's no way I'll be able to manage extra kids, unless you're offering to stay?"

But op doesn't want them to stay!

She wants niece's invited guests only and no extras, children or adults.

Tell the mums your sister has only invited a few select friends to celebrate as it was too expensive to invite more children. If they are doing an activity in an open session then I’d say the mums can book their own children into a session if they’re prepared to stay and supervise. Tell them they can join at the fast food place but they would have to provide their own child with a meal. Or just tell them no, if you and your friend are supervising them the mums can stay home and look after the other child. If one sibling won’t attend without the other ‘that’s a shame if X can’t make it, let me know asap

I think you made the point here yourself

'the party numbers are final and we can’t stretch to additional guests financially' ..... but as it's an open venue then that's fine if you need to bring a sibling and pay for them yourselves for their entry and food.

Make it very clear. Very cf for people to expect you to pay for non invited guests to eat.

You've got great text repsonse to the mums.

On the party bags if wpuld do them!!!
It would be nice for your niece and sister who is unwell.

Total cost is £20-25

Amazon is a good fix for this depending on numbers (im guess its about 12 or so girls)

party bags £3.99 25 bags
Face jewels £6.50 for 12 sets
Paper rock scissors Keyring £6 for 30 pieces
And a bag of mini haribos or something...

It's around £20 if there 20 plus children £25 or so....

9 yo s would be happy with this

As a PP said, there's no need to say "I'm sorry". These people are rude. It's always helpful I think to take I and we out of responses too as it gives people less scope to argue, and simply reiterate what the situation is - i. e. Siblings cannot be accommodated.

So they are being taken out for an activity, food & mums want party bags & siblings accommodated as well!

Fuck me!

As people have said they don't need childcare as they are already looking after 2 kids & then will for the duration of the party have one!

Your BIL has to step in/step up.

They would enjoy party bags but they're not compulsory. Kids enjoy a treat, it doesn't have to be a bag full of treats. Cake is fine OR, if the OP was inclined, I'd pick up a multipack of Haribo from a supermarket and just hand one to each child as they go. Will cost about £2.50 total and save the bother of assembling bags.

OP it's kind of you to do this. Don't feel bad about CFs trying it on

OMG, she is amazing! I always found that when I got railroaded into things it was because I couldn't upset a child, when actually, she has proved the worst that is going to happen is that they are going to be bored.

Edited to say: Sorry, I meant to quote @MPforTitipu !

Given the brazen attitude of these mum's you need to be firm and clear in your messages.
I would put a clear message on the group chat saying
'Amys mum is unwell currently, she is looking forward to seeing her friends. It is a drop and go party and you can meet me at the front door to check your child in at 11am then meet me again at the same door at 3pm to collect them'

Then to the individual mums I'd say something like:

'There's no need to worry about childcare for siblings as it's a drop and go party. If you'd like to stay instead of dropping you will need to stay with your other child/ren to supervise them and cover any of their costs'

These people aren't your friends, you'll probably never speak to them again and they are being beyond cheeky. Shut them down as they will find some loophole or ditch their kids behind your back.

Well, they are going to have plenty of gossip when OP's sister isn't at the party! Honestly, life is too short to worry about what relative strangers, who you will probably never see again once your kids leave school, have to say about you.

They are cheeky bastards, taking advantage of you! Anyone who has kids knows that at 9, parties are drop and run, and that no parents need to stay. Had your DSis asked them to stay? Otherwise, they can look after their own other children themselves. Sausages reply is a good one, or something like "LOL I'm out of my depth already, there's no way I'll be able to manage extra kids, unless you're offering to stay? Obviously there's a budget so you'd have to pay for any extra kids, we're doing our best to make sure Niece has a good day despite her `Mum being so ill. I think entry is x per child, you can pay at the venue, and we're then going to xx where its about x per head. I wish I could offer to pay for all the siblings but sadly not possible."
I honestly am taken aback by the attitude of these parents.