That’s a solid question. if your son is just mildly interested, get them a Duncan butterfly and teach them how to hold it and throw it and do the sleeper and walk the dog and rock the baby and then if they’re still interested after that, then look for a ball bearing yo-yo for them, which I’d be happy to point you in the direction of. You know there’s even a ball bearing version of the butterfly called the butterfly XT maybe that would be a good starter because it gives them exposure to long spinning yo-yos and is also a good just all-around beginner yo-yo