This book maybe a good read and a fascinating read. It may be well written and an interesting story. What concerns me is that for me, the title infers that now we know heaven is real because of the experience of this boy. From what I see in Scripture, experience is not the proof that Scripture is accurate or false because it is very possible to misinterpret our experience/s. Jesus said in Luke 16:31 "... If they do not listen to Moses and the Prophets, they will not be persuaded even if someone rises from the dead" (NASB). Peter writing in 2 Peter 1:19 says that we "have the prophetic word more sure, to which you do well to pay attention..." (NASB). I realize that there is some discussion over what that means precisely, but a very good understanding is that the Word of God is more sure than personal experience (e.g. Mount of Transfiguration referred to in 2 Peter 1:16-17).
I recall reading a number of years ago an editorial from a Time magazine editor who was involved in a horrific car accident in Australia and he was not a believer at all. He claimed to have had an out of the body experience, and saw a bright light, etc., and found it to be a very calming experience. His take away, no worries about the afterlife, everything will be fine. People who subscribe to false cults claim the same experiences. The book "Heaven is for Real" may be a good story and told very well. But for me, the bottom line is that we know heaven is for real because "the Bible tells me so."
Pastor Tom Nelson tells his story of experiencing clinical depression. He talks about what got him there, what he had to do to begin healing, and steps to take to keep from getting into clinical depression. This is a very insightful and helpful story. 
