May I know when can I start brush my kid's teeth ? And what should I use to brush his teeth?

As soon as the first tooth starts cutting through :) You can start with a damp, soft washcloth then just gently rubbing the surface of the tooth and gums! Once LO has more teeth, you can start with toothbrushes - there are several options available but make sure you use those suitable for your LO's age :) We also use Jack N Jill toothpaste, it's fluoride-free and safe for LO if swallowed - always use fluoride-free when learning how to brush, until LO can spit.