To not want my cousin's child at party

We had a family wedding; "no children" was agreed. Some from the other side (bride) were invited, and were not well behaved. Bride was most put out. How surprising! No, not really...
Stick to your guns. You may offend one pair but it's not their party and if no other children are coming they can hardly complain.

I know my aunt disapproves of the way this child is allowed to behave. When her grandmother brought her into the hospital when my aunt was ill she was allowed run wild around the ward.
They're nice people but they just can't seem to see how their child's behaviour impacts on others.

No children means no children.

Parents of the other children will wonder why theirs were not invited. If they cannot find another babysitter, then, regretfully, they cannot come. Mor st least the daughter cannot come although your cousin could attend.

"Oh, what a pity you will not be able to come as we are not inviting children" is all you need to say.

What would your aunt want?

No children is to mean no children. No, a 4 year old may not attend.

Thanks. Yes I think I'll just have to say it would be awkward when none of the other nieces and nephews can bring their children.
Oh dear, I really wish people wouldn't put you in this position

If you have made a rule no children and you don’t have any other children coming to the party you are perfectly in order to reiterate that rule .... surely they can find a different babysitter for one occasion (what if their usual one became ill)
Stick to your guns I don’t thinks it’s got anything to do with the child’s behaviour just that no children are invited

I agree with Missfoodlove - she said it before I could!

Your reasoning is that having this child to the party would be unfair on all the others who aren't coming. And they're not coming because your aunt and many of the other guests are not of an age to welcome hordes of lively children.

Maybe your cousin and her daughter could attend the party in shifts or organise shifts with the babysitters as already said.

We didn't want children at our wedding - a long time ago - and some people took umbrage or just couldn't make arrangements to come, some organised babysitters. So no, YABU.

Just say it would open the floodgates and cause a big problem.
Would it be possible if she and one of the usual babysitters each do a shift?