Hi, I a kinda forum crashing here, I hope that's ok.
I know a little girl who has AFO's, and who, very much like your son, she won't keep socks or shoes on (or for that matter, anything else, if she can get it off... I swear, her mother is a genius with the inventive ways she keeps clothes on her). Having known her for a few years, I can say, the AFO's actually HELPED that because she can't get them off. She only has an AFO on one foot, and once you manage to get it on, with the shoe, its tight and she can't slip it off. Plus, her pant leg and shoe covers up the velcro, means she can't undo it to take it off. Its still hard to keep a shoe and sock on her other foot but the one with the AFO is staying.
Tips I can recommend would be having pant legs he can't slid up easily to undo the straps on the AFO, and tight, double knotted, laced shoes. They are hard to put on at first if they are tight, but equally hard for determined kids to remove. This little girl always wears high tops, which I think also helped keep them on. Also, if he flexes his heel to try to wiggle out, ask about getting 2 velcro ties at the heel. Most I have seen come with 1, across the foot. But I have known people who have a second, around the ankle. It really helps, especially when trying to get them on.
I hope you have a similar experience and can find ways to keep his AFO's on his feet.