HOW TO THINK books entertain and teach at the same time. Drawing, colouring, puzzles, games, mazes, word and grammar exercises encourage children to learn new things and figure out stuff for themselves. Discuss the answers and encourage your child to be creative.
HOW TO THINK books come in four levels of difficulty. However, the age guidelines on the front cover are not set in stone. 
Children, like adults, are all different. Some learn faster than others so you may buy books of a higher or lower 
level of difficulty than that indicated for your child's age group.