MH asked me this last night when I was RSVPing to a bday party for DD.
The party is for a 4 year old from M's daycare. They live in the same neighborhood as us and we've met the parents a couple of times through daycare functions. MH thought we should just drop M off for the couple of hours - I said no. I would stick around since we don't know them that well and I think 3 is still young enough to have the parent there.
What age to you let them attend alone?
Re: What age do you stop staying at bday parties with DC?
I would fully expect parents to be at a 4 year old party and would "judge" if they weren't or just planned to drop them off without clearing it with me first. At least with my DD's party when she turned 4, they were all still fairly needy (needed help with their drinks, cutting food, even going to the bathroom). We had her party at an outdoor park and it involved playground, bounce house, etc. There's NO way I would have been comfortable with 25+ 4 year olds in that situation. Plus, I want to be able to enjoy my kids' parties and not be freaking that every kid might have a problem.
I think maybe once they start kindergarden and the kids (and parents) are all more in a structured environment, I might feel more comfortable, but even then, I'd still want more than just DH and I as chaperones, particularly if it was a larger party.