Yes when he's around me he will masturbate in his diaper and hump things in his diaper around me.
He used to be embarrassed to do it but I told him that it was okay with me if he masturbated in his diaper or humped things in his diaper when he's around me.
Now he's not embarrassed and will hump things in his diaper.
He will sometimes hump a teddy bear, ride a rocking horse, or just hump in the diaper with his hand.
I told him it's nothing to be ashamed about and that he should do it if it makes him feel good.