That's a pretty wide range. At the younger end, something like a Lego kit for a boy (I've purchased Harry Potter Hogwarts Castle and NBA Ultimate Arena in the last couple of years for my nephew), probably Barbie or even an arts-n-crafts sorta thing (make your own jewelry, etc) for a girl. For the older end of the range, unless they're extremely interested in something you know about, don't bother even trying to figure something out, just give cash or gift certs, kids are too fickle at that age to try to buy for without knowing exactly what they want.