Young kids love Capture The Flag. Introduce aspects from that game to create a fun and competitive dribbling drill.
Every player has a ball and two flags. Create teams of 2. Use markers to set up a home base for each team. The goal of the game is to steal flags from the other teams and return them to your base. Players must dribble while playing the game.
Play for a set amount of time and the team with the most flags at the end wins.
Variation: Give each team a different task they must complete in order to win. For instance, one team must get a red & a blue flag while another team must get 2 green flags.
Seriously for all those who coach kids 5-15, watch everything you can on MacKay (lots free on youtube): PVAD, LTAD, block v random, key performance measures, progressions / building on drills, communication...the ongoing work of a genius.
Check his twitter feed too, he posts sketches of things he sees with notes.