If your child is a competent swimmer, you might think about an early season adult triathlon with a pool swim, especially if you (or another trusted adult) can do it as well. Often the open water swim is a deterrent but these early season races tend to be in pools rather than open water.
As your child gets older and more competent with triathlon, consider a high performance team like TAF. The youth level starts at age 13. Explore the 'About the Team' menu above.