ok first the boy:
if it's dinamic, why is the missing knee so low? dinamic means overdramatic. Also the lowered hand should be out more, as boys don't jump like a pencil. The lower foot looks like it's on the ground, so push it up behind the ankle more. Push that foot's knee to the forefront to add a little bend. start with that... it's the foundation.
As for the girl:
Follow through with motion. You have a pretty dinamic pose and the hair shows that she just turned arround, so don't forget the sleeves. They should be twisting that way too... Other than that, that pic is pretty good.