Don't know if there is such a thing. At least I never found one.
I found that a light color pair of sweats worked fine. Not sure how old your son is, or how hands on he'll be, but I started my son out by just standing off to the side and I would call him over to see things. If the hive was not in a good mood I didn't call him over. He is 6 now and wears only a veil and normal work cloths, like Dad.
Starting them young is good, just don't scare them to death with all the protective gear as if you where working AHB (unless you are, and then I wouldn't recommend starting them young
). It is inevitable that they will eventually get stung. Yes the first time can be tramatic, but if it becomes something they are use to verse something they are scared of, the better the chances are they will enjoy beekeeping.
You can also get a white (plastic?) suit in the paint section at Lowe's for like $10, just cut the legs and arms to fit. Just get him a veil (and gloves if needed) and your set.
Here is my son at 5 getting his picture to impress his friends. This was his first hive (a rather small and calm split). I wouldn't recommend the no veil too often though, stinging in and around the face can be painful and dangerous.