(Concern) Child's bad breath

The child doesn't like brushing their teeth.

I like eating, but I don't drink carbonated drinks. However, I enjoy yogurt and beverages like Pororo.

I think I'm just brushing roughly, and my teeth look yellow, and I have bad breath. When I go to the hospital, they say there are no rotten teeth, so I'm wondering why this is happening and what I should do.