The most important thing is to appreciate and enjoy it.
Learning Chess is divided into three big parts; playing, training and studying.

Here is some advice for beginner players:

This is the reason why a child wants to learn Chess. The more you play the better you will get. To improve your chess level, you need to play as many games as possible. At the very beginning it does not matter what kind of games you play (classic, rapid, blitz, friendly etc.), just play and enjoy the game!

Tournament experience is not enough. You need a coach who can guide you and show you your strengths and weaknesses. Initially, the coach can help you understand all the rules of the game (check, castle, e.p., checkmate, stalemate, promotion, touch move, chess clock, play with only one hand, notation, etc). The coach can also help you improve some qualities which you may need to improve on (patience, observation, persistence, etc.) and teach you how to win on simple positions (make mate with the Queen and the King).

This is the only part that children do not lean towards as it bears a strong resemblance to that of their school work. In the first steps, you can try to solve some easy problems (mate in one move, capture a piece, protect yours, etc.) which will help you understand better what you learn during training. You can imagine that you play against an invisible opponent and that in one move you can checkmate.