the 7 is perfect for him up here. he's around 30kg now (11yo) and spent heaps of time on the beach with trainer kites and practising with his 4 and 7.
(like 6 months due to our wet season stingers), so his kite control is pretty good. in up to about 14-15 knots he is ok, but i limit the times he kites to suitable conditions. (strength, direction, tide etc...) he also uses my 9M new in the really light stuff, and can get going in about 9 knots or so... while we are all on the beach

cant overstate how much he improved once we got him a kite that would stay in the sky. made it a lot more enjoyable for him too... (and me). he is basically independant now, and we are having a ball. I also relied on Darren's advice, and it was spot on! hope it all comes together for you both