Safety - I did what Puetz did - and it does put a dampner on (helmet, impact vest sunnies, and a lot of the basics & what if's)- I insisted on swimming competency and some squad training - + what they pick-up at nippers (Surf Life Saving - kids program) is invaluable. 
Unless they have long arms, anything which helps their reach is important.
I found (still do) that having enough bar movement is critical.
Small(er) harness hook, shortened chicken loop, and when it is not too gusty trimming to get the best range.
I went with below the bar depower - but the trade off is it is harder to use compared too a toggle above the bar - but in learning mode they are not using it independently till they are confident on the board.
The seat harness I picked up is not ideal (an opportunistic buy but not really comfortable) but a good one will also extend their reach.
The 6m we started with has a couple of pulleys each side and a moderately complex bridle (SLE) - a few beginners later it is out of balance and although the kite looks good - it has lost its handling. The moral especially on a small kite - choose one with a simple bridal setup - so it relies on the kite design more than the bridal to fly through its stated wind range. - An Ozone is next on my list.
And on the fun / keep the interest up side, 1 of my kids who kites really well now (leaves me in 4 dead), kite tows the other each on their own board. 
Cheers
AP
It also works off the same system as the your regular kite. My girlfriend and I are using them, she's still in the basic stage and where using it for water dragging and she's 60 kg. I'm sure some shop somewhere will let you try one out .
We are getting her the switchblade.
Although it is one year older, it is new.
Plus the bar setup is, IMO, better suited to her shorter arm reach, and gives me more options to adjust the amount of through so she can depower and still reach the bar.
Good luck with that 
- anything to help them control the kite = their reach = bar throw is good.
Let us know progress - my daughter was around 7 yo at 25 Kgs - did not try with her till around 10 yo and not having enough reach on the bar has limited her interest / progress - now ready, she is not a big lass at 13 and that reach is still critical. She wants to buy her own kite .
The plan is finally working - 3 of us who kite soon be able to bias a family holiday destination
Cheers
AP
leave your gear at home!!!put all the time into the kids (sometimes) and the reward will come when they are out there with you, a situation similar to yours i see with our local group, dads out for 2/3 hours then comes in and spends 30 min with the kids. i dont kite but have supported my 13 yo son over several years from buggy to boarding in his sport, a time may come when the situation is reversed and i'm pressured to give it a go..
