In reply to grithugger:
Definitely try before you buy if you can, especially if you're talking 3 harnesses.
I sold a wild country vision full harness recently, the Dad was happy to hand over the cash as it was used twice, no signs of wear, less than half price. But I said to try it first, thinking it was the best he was going to get and a sure thing but then his daughter completely turned her nose up at it. Luckily he had a younger son who was beaming with it on so bought it anyway.
Same thing happened with one of mine, bought him a petzl horrendous but he barely tried it, I'd have insisted he use it if he didn't already have a wc elite ultralite that he was happy with (although he wasnt happy with that at first!).
If they fit a sit harness and they're happy with it, I'd get them one at that age. You can't teach really belaying in a full harness. If possible I'd get a threadback as well because it's much less likely to get fiddled with. Plus they need to know about them for nicas.
The Wiz Kid is only £30 at Decathlon, though.
Clog centre harness is a good option, it's big enough for adults too but lacks gear loops.
Another alternative is a separate chest harness, camp do one and there's an edelrid one on the auction site for £14 ATM.
Post edited at 00:02