Dogs always show signs of jealousy between any pack member, as you have just said you're pushing him out why wouldn't he become jealous.
I've always involved my dogs in the family, giving them no reason to be jealous. In fact I would make extra fuss of them so that they still feel wanted, not put in the yard when the boy's about, that will really feck him off.
It's always hard to pass comment in this situation, none of us know the dog, it could be proper nasty and then I would certainly take him out back to meet his maker.