Q: "A young girl exercises on a treadmill." Does this mean that "A younger female is using her legs."?
A: yes

Q: "A child reaches the bottom of an inflatable slide." Does this mean that "a child is reaching the slide"?
A: no

Q: "A young boy jumping in a jumping castle." Does this mean that "A kid in a bouncy castle."?
A: yes

Q: "A male surfboarder on a yellow and orange surfboard rides a wave." Does this mean that "A man is wearing a black bodysuit as he surfs."?
A:
it is not possible to tell