If your child is in kinder or close to, it might be a good time to research for an electric toothbrush. I found one I really like and Amazon currently has a $10 coupon to click on the page so it is $20 off the regular price for a moderately affordable $29. I got it for LO for Christmas and she had fun personalizing it. The related app helps her to remember to brush on her own and brush a long time with visual cues and short lessons. It is connected to an app where when she cares for her teeth it gives all kinds of video game like stickers/enhancements to reinforce good habits. When she forgets to brush, her little Sparkler looks so pitiful and sad. Good motivator in so many ways!
Philips Sonicare for Kids Bluetooth

https://www.amazon.com/Philips-Sonicare-Rechargeable-Toothbrush-HX6321/dp/B00YAR7ZL6/ref=lp_10586016011_1_12_a_it?srs=10586016011&ie=UTF8&qid=1484006631&sr=8-12&th=1