We have been teaching our 12 year old to sail for the last 8 years,
We have done a few trips to Maui and had her enrolled in windsurfing summer camps that have been invaluable, so I agree that learning to sail with people your own age is a definite plus!
We have also never forced her to sail, always offered to rig her sail and get her board ready, its totally up to her. Usually if there are other kids are around she will get in the water, she is keen for other kids to have a crack with her gear,
Make sure the rig they learn with is light and easy to chuck around, Phoebe started out with a Ezzy kids rig, then we hoped her up with an S-1 Severne 3.0 rig, both rigs are super light and pretty tough (especially the Severne)
Phoebes first board was an RRD 160ltr Orange thing, aircraft carrier in width, but great to learn on, she is now on her own 115 lt. young gun, learning to water start, but loves cruising around on her SUP
I think correct gear is half the challenge,
As was previously said, make it fun, make it safe and get involved with them,