How to teach kid's a routine to make sure they are brushing every part of their mouth in the most effective manner? Any videos or tips on how to do this?

By doing it with you lo everyday!!! I have been doing it together with my 3 year old. And i make it fun. Ill sing a song and make silly faces whilst doing it with him. Its hard to ensure they brush every corner. For a start at least they are brushing. Many kids, dont even want to brush!