As MHB said, apples are to sweet. And you would essentially need to use heaps of water and a little apple to get low ABV. It's very hard to stop a fermentation in its tracks, unless you pasteurise really. Even KMET and Sorbates don't really stop fermentation but inhibit it from starting back up.
If you went with low apple and mainly water you would just end up with an insipid watery non apple flavoured drink.
My suggestion of Kombucha is that, it's pretty easy to do. You can buy ready to go kits with the scoby and all. It's very low alcohol (my nieces love the stuff and are 5 and 7) it tastes great, you can mix juices with it post ferment if stabilised, or mix fruit in pre ferment. And it's great for you (apparently according to imahippieandwearatinfoilhatvacinescauseautism.com)
Other than that, I guess you can get him involved in the regular home brewing, and buy the Carlton Zero etc for him to have, and don't give him a sample or two of the real stuff because that would be wrong. Tasty but wrong.