It's a difficult situation--I teach snowboarding full time when it's brisk, and so I'm on the mountains about 100 days a year in the winter. In the off-season, I split my time between skating and hoops... You see a lot of these kinds of "landing area" collisions where person A is trying to land something and person B ends up unwittingly getting in the way.
The kid should've probably had better situational awareness, but he's a little kid. So no real blame there.
The skater should've probably checked his landing better and made sure it was clear before he started, but its an understandable mistake when you're trying to stick a landing on your X-number try. So, no real blame there.
The mom shouldn't have hit that kid. She's a creep.