How often to brush toddler's teeth?

I'm very conscious of over-stepping since the toddler is my 3.75 year old neice, not my own kid. Her parents are split up, so I only see her when at my brother's (her dad's), but he never brushes her teeth before bed (and she was eating just before that). She even has a little rotten/brown tooth at the bottom front of her mouth. She's never seen a dentist either. When she spends the night at my place or elsewhere, her dad never packs a toothbrush or anything (so I bought one for her and she LOVES brushing).Her dad says it doesn't matter since the teeth are baby teeth, but it seems weird to me. I feel the benefits are a clean mouth, good oral hygiene habits, and a night-time routine (he just puts her to bed in the middle of playing, maybe with one book to read). Am I looking too much into this? I imagine she SHOULD be brushing her teeth, but maybe this is normal for toddlers, I don't know. via /r/Parenting https://ift.tt/2OTTWHI