Your Kid Needs A Good Piano Teacher
Your kid needs a good piano teacher because piano is very hard to understand. Piano requires navigating multiple planes of information at dazzling speeds. It is both physical and mental. Ingenuity is the only way to teach such a difficult subject. Kids are naturally artistic and their minds flow easily into creative decisions. Watch kids playing with toys and you will see imagination and effort personified. Kids do not have the organization and ability to see the road ahead. This the teacher must supply. More than anything a piano teacher must be patient enough to unlock this natural, childish ingenuity. It can't be forced. You'll have to be ready to make tangential interest into something more, by any means except pressure and guilt.
Giving Kids The Knack
Kids get interested when they think they have a knack for something. One of the first tricks you must perform is to lower the bar far enough for the child to feel some confidence at the keyboard. Unless you do this, almost all children will feel lost and frustrated.
Notes Before Fingering
Suppose you are teaching a child Jingle Bells. If they reach for the correct keys with the wrong fingers, do not stop them. Why? Because they are smart enough to find the notes, and you should be happy with that for a moment. Only when they feel comfortable should you broach the idea of better finger organization. If you stop them with endless finger corrections you stop their burst of ingenuity. If you let them keep going, they have the reward of playing the song, and the reward of your praise.
With those two rewards in hand, you may well be able to go further with the idea of fingers, perhaps not. If you put the child in constant touch with their ingenuity, they will practically teach themselves fingering. The only fuel they need is songs they love. It's up to you to decide when to interrupt their work-flow with further complexity.