What tactics books should my child use?

Susan Polgar's books can be used as introduction. Both are easy reading.

• Chess Tactics for Champions: A step-by-step guide to using tactics and combinations the Polgar way
• A World Champion's Guide to Chess: Step-by-step instructions for winning chess the Polgar way

If s/he doesn't know tactics, s/he can also use

• Learning Chess Step 2 Workbook (500 problems)

If s/he know tactics well, and wants to improve, use two classics:

• 1001 Winning Chess Sacrifices and Combinations
• 1001 Brilliant Ways to Checkmate 

If s/he wants to see tactics in real amateur games, use

• Tactics Times (1000+ problems)
• Tactics Times 2 (1000+ problems)

I have other books also recommended at: ​http://www.completechesscourse.com/books.html

And the following 3 software should be mentioned:

• Chess Tactics for Beginners 2.0 (1000+ problems)
• Chess Tactics for Intermediate Player (1000+ problems)
• CT*Art (1000+ problems)

All software are available at my online store: ​http://www.completechesscourse.com/ministore.html#!/Suggested-by-Coach-Andy/c/13271858/offset=0&sort=normal
(Chess Tactics for Intermediate Player and CT*Art are available in the same package: Training Package for Intermediate Players)