I know that if you have to ask it probably is, but.....
would it be rude to indicate on the back of my daughter's birthday invitations to classmates "due to limited space, no siblings please"? Is there even a nice way to say that? I would do it discreetly on the back of the invite.
It's just a bit uncomfortable because I don't really know a few of the parents from class BUT there are a few who have been known to bring younger siblings to other classmates' parties (even though they technically were NOT invited).
I normally wouldn't care, but the place we're having it has limited capacity, as does the transportation method I've arranged.
My other option would be to tell these people in person, but I feel that would be contrived as well, since I don't know them all that well.
I suppose I could JUST put it on the couple that I am worried might do it.....and leave it off the others. I mean, I think for MOST of us, it goes without saying, but that hasn't been the case with a couple of these families.