Use the same short instruction
Show them, then say “spit into the sink.” Keep swallowing or tasting toothpaste out of the game.
Put the toothpaste on the brush yourself
Use the amount the tube directs. For Tooth Wizard, that is a pea-sized amount. Put the tube out of reach after you have finished.
Tell the dentist what is difficult
Explain whether your child swallows the paste, has trouble making the movement, or dislikes the taste. Those details help the dentist give advice that fits your child.
