I think my most favorite scripture is "...by small and simple things are great things brought to pass; and small means in many instances doth confound the wise." Alma 37:6-Book of Mormon. I've been teaching my piano students that one of the "small and simple things" they can do to become a better piano player, is to practice their note reading flashcards 3 minutes every day. Those students that know the names of the notes can sightread faster, learn their pieces faster, and progress faster. And all it takes is 3 minutes every day.
If your child is learning his notes, don't have him learn the whole scale of flashcards from bass clef C up to treble clef C above middle C. That's too much to learn at once. Start with 2 flashcards, and when he knows them, add a third. Then a fourth note and so on. Start with just the treble clef notes first, then add the bass clef.
The brain stores this information in two different places in the brain. You can show your child a flashcard and she can easily and quickly play it on the piano (or other instrument). But to have her SAY the name of the note is a whole other brain processing skill. So when practicing flashcards make sure your child plays it AND says the note name.
Children learn in their own special ways. Some children easily pick up on learning "every good boy does fine" and that helps them learn the note names. Other children process and understand the note names when they realize the notes are in alphabetical order. Still others just can't remember them at all! When this happens I try to "hook" one of the note names to a person's name in their family. For example, one of my students-Greg-could not remember the note names at all. I showed him where the top space on the bass clef was and said, "that's your home. Look at the top space and always remember that is where you live--G for Greg." Once that was established (after several weeks) we could branch on to neighboring lines and space names.
Recently one of my students noticed that the bass clef top space, top line and space above, spelled G A B. For him, that will be the hook that will help him learn his notes--I hope. If children can discover a pattern or hook, it becomes theirs to remember forever.
There are several sites where you can download free flashcards. http://linkwaregraphics.com/
Children LOVE games, so play games 3 minutes a day during practice time and see the improvement!