I saw this in a Martha magazine last year. Made them all last summer and tis the season again! Sorry that it isn't really a "recipe" but it was so easy that I never wrote it down...I just wing it.
Watermelon Popsicles
Seedless watermelon, cut up
In a blender, blend the watermelon until smooth and then pour into popiscle molds. Let freeze and then give to the kiddies. (I had some left over pureed watermelon and the kids drank it for breakfast - the guzzled it down!)