Zoey: The Big Eater

One of our sweet little kittens is really packing on the pounds. I noticed this just the other night. All three of them, Isabella, Obi-Wan, and Zoey, were all sitting on the floor side by side (They are all growing like weeds too!). Suddenly I noticed the Zoey is, shall we say, a bit more portly than her siblings. She's to the point where she's developed belly "waggles" underneath. She's not even quite six months old either!! Looks like she's in for a kitty diet. I've never tried to slim down a young kitten. Should I wait until she's older and see if she slims down? Anyone have any advice?