To brush teeth for a child in Engpsh, you can say "It's time to brush your teeth." or "Let's brush our teeth now." To give instructions, you can say "First, wet your toothbrush and put toothpaste on it. Then, brush your teeth in a circular motion for two minutes. Make sure to brush the fronts, backs, and tops of your teeth. Spit the toothpaste out and rinse your mouth and toothbrush with water when you're finished."