With my DS2 i mimick what he needs to do so i will open my mouth nice wide to show him and it is a bit of game that he does what i do and explain everything what i am doing like i will say i'll do your top and then bottoms and then i show him how to clench his jaw shut but keep his lips open so i can give the front of both top and bottom a good scrub. Also i have just recently been to the dentist with DS1 and she explained toothpaste should be treated just like a medicine as flouride is quite dangerous in a large dose and then a child should only use toothpaste until they can understand to spit it out and rinse. If you notice on an older child the real white patches it means they sucked on toothpaste as a younger child and can cause the enamel of the tooth to become brittle.