The book's title is slightly misleading. The subtitle is a more accurate description of the book as Kushner spends most of the book telling parents what he thinks God is and isn't.
The author at times seems to equate God to love, charity, good will, etc. and then conclude that since love, charity, etc. are real then God is real. What is wrong with leaving the definitions of these words he equates with God alone? Why not let them stand on their own definitions without dragging a God into the picture?
Kushner's definition of God is very confusing and contradictory. It didn't make any sense to me, and I don't see how it could make any sense to children. On the other hand, the book does have many good teachings for children on respect for others and their beliefs.
Most readers will have problems with much of what Kushner has to say. Theists will find him far too liberal and atheists will wonder why he tries to consistently bring God onto the scene. I imagine that many people who have read this book have actually become atheists since he does such a good job of showing how the notion of a personal God is absurd and outside the realm of our daily experiences. I don't think Kushner would want this to be the result however, as he says that it is better to be a fundamentalist who takes myths literally than to be someone who rejects stories for their mythological components. I strongly disagree with him on this point.
He also makes the bold assertion (on page 138) that "Human wickedness is the result of living without God. . .". That is hardly the kind of answer I'd want to give to my son when he asks about God. What sort of self-esteem will that give him if he doesn't believe in God? Why call someone wicked for their unbelief? Shouldn't their actions (rather than their belief or unbelief) determine what kind of person they are?
The author makes such statements as: "To the extent that Man uses his intelligence and develops his conscience, he turns to God in order to reduce chaos and misfortune." (p. 78) I think just the opposite is more true. When people use their own intelligence and common sense, they are not turning to God or some supernatural force. They are turning away from such superstition and relying (correctly) on reality (which is all we have).
Kushner falls in the common theist trap of giving God the credit for everything good that happens and claiming that God had nothing to do with bad things. He does improve on the normal continuation of this thought that when something bad happens it means that we are sinful. He claims that such a sentiment which causes people to blame themselves for things out of their control is false and harmful to children (and adults). Of course, I agree with him here, but I also think that giving a God credit for the good that happens can be harmful. If we don't understand that good happens because we make it happen then good will not happen nearly as often.