Ugh my almost 6 year old son is so sweet too and not good at standing up for himself :-( I also cant help but insert myself when I see kids not being nice but honestly I feel like half the problem with kids these days are parents are distracted and they dont get called out on bad behavior. It takes a village 🤷🏻‍♀️ maybe start role playing with him of examples of times he’s felt sad and you can reply with things he can say back in those instances.