Well, having experienced being 10, sitting on my porch, waiting in vain for
anyone to show up to my birthday party... I didn't leave anything to chance when it came to my kids' birthday parties. The first invites went out two weeks ahead of time. Then about 5 days before the party, I would call every parent on the list to personally confirm whether they'd be coming.
I was always pleasantly surprised when someone RSVP'd. Most didn't. And even those who did weren't guaranteed to show up. Typically, with larger birthday parties, only about a third of the invitees will show up, even when their parents say they'll be there. Small groups of close friends are more likely to all make it to the party.
Some parents seemed a bit bemused that I'd call them. But I will say though... My kids never had to experience a birthday party where no one came. So I'm pretty proud of myself for that!