Good on you, well done. Got to be patient but it's super satisfying for them when it comes together and they nail little milestones.+1 what Mark said on the wave sail, works well once they get to a certain level. Light and easy to handle if rigged well.
We started my son on 2.5 to 3.5 Neil Pryde Dragonfly's which were pretty good although a bit too floppy in the end, didn't react that well to lots of downhaul the way an adult sail does. Mast is quite soft. He used Duotone Hero sails around 3m and a 69L board here. Had fun, learned quickly.
This was taken over about 10 days the wind in the second half of the vid, 2:30, on was fantastic.
k.