The Piano Is A Child's Thinking Machine
The piano is a child's thinking machine, actually much more effective than computer games for learning. Pianists solve problems constantly. Playing the piano will teach a child how to think and how to concentrate on a task for a few moments. Thus a child playing a song all the way through is a tremendous victory of ingenuity and perseverance. It takes a lot of concentration to learn all the parts of a song, and deliver them largely without flaw.
Any effort by the child should be praised. Piano teachers should rely on memory and a sense of the keyboard rather than reading music. This is because reading music is entirely too complex to be thoroughly enjoyable. Concentrating on that alone defuses the childish enthusiasm necessary to be inspired.
Find Songs The Kid Likes
Playing familiar songs is a far better child's introduction to the keyboard. I'm not saying, "Don't read music." I'm saying, "First interest the child in aspects for which they will have a natural affinity." Reading music isn't often one of them.
Kids Are Very Agile
Asking a child to think about their hands and fingers in relation to the keys is a natural task. Asking a child to decipher arcane musical notation is completely foreign to them. Deciphering notation when they're not familiar with the keyboard is a recipe for confusion and disaster. Children are naturally ingenious, and love to solve puzzles if they are fun.
Think of a child about to ride the "bumper cars" at an amusement park. Would it be better to simply let them ride the car and see what it's like, or should you deliver a lengthy lecture about traffic safety, citizenship, and electricity?
Show Kids The Physical Logic
The only way to unleash most kid's genius at the piano is to let them first understand it on the physical level of hand and eye. That is where they naturally think. To insert the written note prior to that exploration is foolish. So kids will be more comfortable if you make the first hurdles at the piano physical and mental, rather than limiting to the extremely cerebral realm of the written note.
After all, most beginning child pianists have solved few enough problems, and the piano rewards the solution with the ability to play a song. Doing your math homework has no immediate reward to a child. Learning a song does.