I was filming my son in the park a couple of weeks ago and actually got a video of a crash into into a kid (maybe 5-6 y/o)- the parent stopped with right at the end of a rail, but everyone was expecting them to keep going. My son didn't see them until he was up on the rail and had to bail - was a good crash scene, but that's because no one got hurt. The 5-6 y/o ending up crying and the the father blamed everyone else.
Unfortunately not everyone knows/respects that parks are for action. Taking small kids into a park area is dangerous at worst, inconsiderate at best. Gotta say though that it's hard to get them to understand when the park users are just sitting on the jumps though - gives the impression that it's a slow-paced area. (Skiers are worst where I ski, but sounds like that might be unusual in the U.S.)