Asking a child a specific pose can be a bit tricky. It can work better if the shooting is perceived as a game, it's good to leave some space to the child, let him/her express himself and do what he wants. You can also use some of his toys as photo props. All of these will help. You'll want to give some directions, but also let the child do his own things too.
Using your camera high speed will also help you capture the best moments.
Here is the result of a recent shooting.
Author : Rev'elle Photo, Lyon based photographer (France), http://www.revellephoto.fr