Well Lindsey, let me get this straight, a kid ran at you full speed, threw the bag of food he was carrying into your lap where you were holding Harley and he growled and screamed? You dang skippy he did, who wouldn't, most greys do not like small children for this very reason, they are too quick moving and loud.
I don't think Harley will be traumatized for life but he will certainly remember that particular kid for a while if he sees him again. I think he will be fine Lindsey, that would have scared most people much less a grey baby, Harley was just reacting to the situation.