In Amsterdam, bikes are all over. They're parked out in front of shops, they're being ridden all over, and they're even in the canals (oops). There are kids, adults, adults with kids, adults with adults, and even people with dogs on bikes.
We saw many interesting combinations, including the mother and son below. He was standing up behind her on the bike. I just about had a heart attack for him, considering that he wasn't wearing a helmet. Heck, I only saw a few people wearing helmets the whole weekend. It must not be an Amsterdam-ish thing to do.