Why? Computer! Chess software have greatly shorten kids' learning curve. If you are still working with books and board exclusively, you may want to check out this new powerful tool.
Normally a computer software that trains tactics contains more than 1000 problems. It can track your child's progress, measure his/her problem solving skills, and create quizzes with randomly selected problems to test your child under time pressure. Your child can repeat his/her practices with the software in different ways. There is no need for setting up a board, which consumes a lot time. Often, the younster already sees the solution before the position is setup on the board. There is no need to flip to the end of the book for checking answers. When your child makes a mistake, s/he will also get some hint on screen to correct his/her mistake.
How much do all these conveniences cost? $10 to $20. Not more expensive than a chess book.
There are a lot of chess software available. From my personal experience, I recommend ChessOK software. They are adapted from Russian chess books, and consists trainings from tactics, endgames, middlegames, strategies, to openings. I am working on organizing my recommandation list on the "Software" tab of this blog.