If you’re into the idea of letting your son just play the keys and it’ll sound good no matter, anything with scales will fix it for you, which none of the Model:Samples do. Also, go for polyphony. Monophonic synths are cool, but for someone who’s starting out, the idea of single note lines might seem a bit abstract.
I’d go for the Novation Circuit. Great scales, extremely playable and it has synths and drum samples to go, and it’s a very immediate playing experience. It’s portable, battery powered and given its no screen, marco implementation, you don’t need to know much about music, synthesis or anything cause it’s so abstract and it’s got enough short cuts to piss off old synth vets, it’s really tailored for people who just want to dive in and get going, no matter their preference.
However, no scales or auto corrections in the world will replace the value of just a few piano lessons or guitar lessons or similar. Even if you never gel with an instrument, just understanding how it works on a fundamental level, will provide you with so much more, no matter. You don’t need much, just get an idea of it, and everything will make so much more sense and be more coherent. And you can readily take such a class while you’re banging away on a Circuit and even bring the Circuit to class and say. “Hey, you talk about C minor like you’re all that, but can you show me you got what it takes when the going gets really tough? Huh? Can ya, Teach? Or are you just a D flat spineless piece of kazoo player, like your useless father before you.”