Peter asks: How much do you spend on birthday presents for your kids' friends?

Well, we've officially entered the "birthday party years." I figure it's a place we'll be in for the next decade (and then some). Not only will it mean that we'll have to stop being so lazy and go from family-only birthday parties to bashes with school chums, but we'll also have to start preparing for the barrage of birthday invites the kids are going to get from their friends.
 
Addy is beyond excited about attending her first kindergarten friend's birthday this weekend. Her pal is turning the big 05, and she was invited to a local play place to celebrate.

Obviously, me and Lisa had a bunch of questions. At five, we figured parents would be welcomed to stay and keep an eye on their kids. (I can't imagine the birthday girl's parents would want to be responsible for the whole class — she invited everyone — anyway.) Little S's mom confirmed that with Lisa the other day at pickup. She also said that siblings were invited too, which was a nice surprise, since Addy asked if she could bring Peyps, and Peyton has been talking non-stop about the party since Addy brought home the invite.

One of our biggest questions is about presents. I have no idea what's acceptable to spend on a kid (who isn't your own) for their birthday. And what the heck do you buy the kid? (The only thing I know not to pick out is something that makes noise. Noise-making kids' gifts are nothing but cruel.) I'm sure Lisa will pick something Disney princess-y, but she doesn't really know what the kid likes, and Addy's no help — she suggested buying a yellow dress and a unicorn.

For those of you who've already entered the decades of birthday parties, how much do you generally spend on gifts? And what's your go-to present for kids you don't know very well?