Wee-man is in a baby carriage. (Carriage is on a huge hillside going down hill, busy sidewalk)
"Daddy" (Jack-Ass character in disguise) asks for directions from someone.
With a gentle push the carriage is rolling down hillside.
This scene is also filmed from the perspective of Wee-Man looking out for first person perspective adding to the 3-D effect!
(added fun carriage has controls to actually speed up/slow down & turn.
Watching people chase it down is the prank, the jackass part is this is just crazy/dangerous enough already for let's say someone to cut the breaks?