If you want something really, really easy for a 9 year old, you could do the pond at Graylyn. You're going to laugh when you pull up, because it's not much more than a puddle. But it has a lot of bluegill in it, a few large mouth bass, and there are no trees around it so it's very easy for a kid to fish there. Just get some worms and you're guaranteed to catch a lot of fish. And the folks at Graylyn are OK with people fishing there. You could also go around the corner to the small lake at SECCA, for a slightly more challenging, but still pretty easy, fishing experience.
CG Hill in Pfafftown and Village Point in Clemmons are two bigger lakes that are easy to fish. Plus, in the next few weeks they'll get stocked with trout, which are fun to catch.