My advice would be to get something like this, and help them out with setting up the plane. Fly it yourself first, as it shouldn't be insanely difficult, and it will make sure the plane flies well when your son tries it. If he gets good at it, you can get him one of these.(https://www.horizonhobby.com/product/carbon-cub-s-2-1.3m-rtf-with-safe/HBZ32000.html)

(https://www.horizonhobby.com/product/aeroscout-s-2-1.1m-rtf/HBZ38000.html)

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Also, make sure to not completely drain batteries, and to not leave them inside of the plane when not in use, because doing so will destroy lipo batteries.