My 2 eldest kids started on a 1.4 meter square foil at 5 years old and essentially flew it after a couple of minutes instruction. The only times I had to help them was to restart it when it "fell" out of the sky during a lull. My daughter started flying revs at 8 and can fly but isn't interested in tricks. All 3 kids (3,6 and 9 now) will fly a SLK for a while, giving slack and making it dance.
Start off with a "best flyer" single line and get a small foil dual line too. As they learn to crash less, go on to a stick framed kite.
I try to fly as a family, which can be frustrating at times but ultimately very rewarding.
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