The Kindle edition of Heaven For Kids by Randy Alcorn is currently available for free from Amazon. This book is written for children ages 8-12 and answer many of their questions about heaven at their level of understanding.
Thanks to Clip With Purpose for the link!
The Kindle edition of Elisha's Bones by Don Hoesel is currently available for free from Amazon.
If you don't own a Kindle, you can download these books for free by downloading Amazon's reading app to your computer or mobile device.
Note: Be sure to check the price before downloading; the price may change at any time without notice.