My son is 11 and when I began to notice him getting aroused in public I immediately changed his wardrobe. I bought him baggier pants (old navy has a loose fit that is really comfy) and longer t shirts. This concealed the problem but we still wanted to address the issue so when we would notice it we would say the phrase "you need some privacy" and lead him to his room or the bathroom. With lots of repetition he now gets the cue and knows what to do. He usually will go and play with one of his fidgets (slinky or ball) then comes back. So basically a redirection.

This is really hard because he has very limited vocabulary and still watches mickey mouse and plays with hot wheels....i am sure he will never read, just wondered if there was meds for erections and such for a 13 year old going thru puberty and he hasnt a clue to whats happening to his body.