Is this what I get for trying to please everyone?

[EasterJoy]

I agree with this. Especially with children, when it includes staying overnight, I can’t imagine visiting someone and not knowing who else would be sleeping in the house. Depending on parental levels of caution and family dynamics, some parents wouldn’t let their children stay overnight with opposite sex kids - even if they are cousins. Even if I am having guests over for a short time, I always include who else I might be inviting, as the dynamics can be wildly different with multiple guests as opposed to one guest or one family.

That said, obviously, you were surprised by your first nephew’s request, and it is understandable that when plans change, and you think everyone will be ok with the new plan, you might forget to go through that process that you originally went through with the initial invitation.

So on the one hand, it would be understandable for the kids to bow out gracefully, or for the parent to say “I’m sorry, I don’t feel comfortable with a sleepover if there are other kids there too” or something like that, they certainly don’t have to be rude about it.

And on the other hand, while I understand that they might be frustrated that the terms were changed from something they were excited about to something they don’t think they can do, they should also be understanding that you didn’t plan it this way, and that you made a simple mistake of thinking they’d be happy with this arrangement, and that you are stuck in the middle of a problem that isn’t really yours.

If I were you, I might apologize for not thinking to check with them before you okayed the extra night. But I would also expect them to be gracious and apologize or express regrets to you since they know you were trying to do something nice for them.

This. “I’m not comfortable with other kids being there” is sufficient. We unfortunately know that cousins do assault each other–I don’t just mean sexually, but even emotionally, verbally or physically–when they’re not being supervised. The OP probably couldn’t supervise all three all of the time.

Yes, using the “retrospectoscope,” it would be preferable to say, “Sorry, John, but I don’t want to put your cousins on the spot to ask them if it would be OK if you stayed on. You got your time as planned, I’m going to give them their time as planned, because they probably would not feel comfortable saying anything that might sound like ‘we don’t want him.’ I may ask them if they’d be interested in something together with you in the future, but I’d have to think about that, too. We’ll see. These visits do take a good bit of energy for me, and I like to have just a few of you at a time so I have some time to talk to each of you. For this time, though, we’ll stick with what we had planned.”

Adding guests was her choice, however, provided she notified others in time for them to change their plans if they had a problem with the addition, no questions asked.