Sarah,These are really strong, in their pose staging and silhouette. I like that you are really thinking of these in terms of stages of action.You're using the hands fairly well - I would just suggest to develop them a little more in terms of reflecting the psychology of the character. The landing on the swing set, I'd consider showing a little more of a 3/4 pose in the hands - they get a little profiled and lose their silhouette.Good character, too.
I agree with Patrick. Also on the swing jump action, on the last pose it might help to squash him down further, bend his knees more, and then add in an extra drawing of him standing up a little straighter (even though we were only supposed to do 4 drawings).