because they can - it's a bit of a challenge - ceiling must be reasonably low for them to do it

Try it it's fun, jumping is the closest thing people have to flying without any equipment, so it's pretty liberating, why do you think people like dunking basketballs, parkour (free running), and bungee jumping? It's pretty liberating, at least jumping to touch the ceiling is safer than bungee jumping, never touched a ceiling but I did get an exit sign that was about 9ft up. That was fun, if I do it now it'll look weird. Too old

they seem to do that all over. it's not uncommon. when they get taller, they stop or maybe it's more mature. it's like jumping in a puddle of water. it's there so do it.