“If it turns out the kid is all there,”
All there? Dude! The kid has cerebal palsy he has not been “all there” since birth!
Actually, a quick check says that the mind is only affected in roughly 1/3 of the cases. That means in roughly 2/3, the person should theoretically be accountable, at least enough to understand “Hitting is bad, and may result in others hitting back.”.
A wheelchair or a movement disorder aren’t automatic indicators of a lack of intellect or understanding.