I would also say that cameras were probably not that common to be held by kids back then either. I would say there is a good chance whoever took the photo was an adult as well.
Oh for sure, it's just that this particular image and especially that particular ramp don't look all that feasible. The leg on that thing appear to be a brick on a cinderblock on a milk crate.
Adult? Well... that's Uncle Charlie. He smokes a lot of some funny smelling tobacco, but he's cool! He knows a lot of things like how to fix cars, how to collect baseball cards, how the government is spying on everyone, how to get lucky with the ladies, and he helps us with our math homework. He also says our neighbors are "commies" but I'm pretty sure their name is "Connor". Right now he works at the meat packing plant, but he plans on going into management (whatever that is) once the right opportunity comes along. He says the secret to his success is growing a real thick mustache. Really, more of a big brother, yanno?