Oneill makes sizes all the way down to a youth 4 maybe even a 2 that are their "hammer" models and are designed just like your standard wetsuit. I belive they make them in spring suits and full suits. Check your local dealer or hop on the website.
Both Rip Curl and Oneill make wetsutis down to size 4 that are built just like adult suits. Just depends on what features you want and how much you want to spend. But fit wise we've had great luck with Oneill for kids. We stock the Hammer 3/2 and Epic 3/2 GBS