A friend and former Harbor attendee recently asked Mark and me how to tell kids about heaven, hell, the New Heaven, the New Earth, and theology surrounding life after death. We've received this question a few times, so I wanted to share our answer here.
I think many adults dumb down theology for the sake of kids and that's really not necessary. I honestly think it's best to tell a three-year-old about heaven (and hell for that matter) the same way I would tell a 30-year-old. Obviously the nuances and feedback will be different and the conversation will take different tones, but really, it's effective to tell kids big truths. It doesn't make sense to water down the truth when they're young, only to have to bring out the real truth as they age. Even if it's totally over their heads, they'll grow into it. It's beneficial for them to hear you say the same things over and over and over.
"The Jesus Storybook Bible" is a great tool for any parent, aunt/uncle, friend. You can look through the table of contents there and pick out some helpful stories.
"Big Truths for Young Hearts" is awesome. It's most useful to read to kids who are ages 8 or 9 and older--or it's great for an adult to read to be prepared to talk to kids (or really, just a systematic theology overview for an adult).
The Randy Alcorn books on heaven are amazing. We often give "Tell Me About Heaven" to our peers and friends who have kids when a loved one dies. There's also a book by Alcorn for teens and pre-teens to read and finally "Heaven" is a 500-page book on all that the Bible has to say about heaven. I love, love, love it and have read it a couple times. It really opened my eyes to the truth of heaven after being a believer and bible teacher for about a decade. It's good stuff.
I'll close with noting that this issue really falls under a bigger umbrella--should we tell our kids the truth or shelter them from it? Or perhaps, should we tell our kids the truth or should we participate in make-believe and break it to them later that we were lying? Barring traumatizing my kids with truths that are too violent for their to hearts to bear, I always err on the side of telling the truth.