Hahaha everyone is hating on the OP so hard, but I remember a thread that was probably 5 pages solid people hating on gapers/racers/posers in the park not long ago.
These people piss everyone off, but when the kid is that young it's clearly the parent that deserves the blame. The kid is just having fun riding through the park, it's not his fault at all. In this case though there's nothing wrong with the parent's move either. It didn't look busy, and the kid didn't cut under a big jump or anything. As long as the kid has proper park etiquette then there's nothing wrong with being in the park having fun. That's what the park is there for...