I don't see what is childish about the belief in Heaven being a physical place, especially with what we've come to know about the vastness of the universe and how little we really know about the universe.

This is much different from God with a beard.  It was witnessed by the apostles and described in two gospels and Acts.  Jesus said his kingdom was not of this Earth.  

Are you a Christian or an atheist?  It's hard to tell.