At 6 months old, your Yorkie is still learning how to play. Getting him at 7 weeks, he missed some valuable time with his mom and littermates where they would have learned how to interact during play. Sometimes kids are a bit aggressive for these little breeds without meaning to be. These little guys will do what they have to when they feel threatened and cannot be blamed for that. I would make it my responsiblity to make sure the kids are engaging in play that does not make the little guy feel threatened.
Maddie is very cautious around small children because my niece got too rough with her when she was a pup. Totally, my fault. Maddie snapped at her, but she felt she was in danger. I hope you are able to resolve this and it doesn't come to rehoming you little guy.
