youth safety harness?

[KOOK68]

I hunt out of a 4 legged platform stand. the legs are pretty much vertical, with triangular shaped rungs welded on. That having been said, I'm looking for a youth sized harness. I guess it would need to have a short line, with a caribiner that I could to attach to the next rung as he climbs. He's 5, and I just dont trust him climbing w/o a safety device.
The rungs are rounded, so no chance of getting stuck or cut if he slips. I have never used a harness, so not sure what's out there.
Any advise?

[Lefty]

HSS Lil' treestalker is what my daughter wore when she was younger.  I would highly recommend it.