Explaining heaven

Picking up my son from school. A little girl was waving at me. I ask,"Tommy who is that girl?"  He says, "Mom she cwys everyday in the early room. It is so annoying!"  I say," Aww she must miss her mommy. Maybe she doesn't understand she will be back." He says, "Yeah i remember crying , cause I thought you were going to heaven." I say, "You thought I wasn't coming back?"He says," Naww I was sad cause i had no friends."