"Heaven" to my 4 year old

Treycen is at the age where he wants to know everything and I am having a hard time trying to explain things in a way where he will understand them...  For example my grandma Goold has just passed away and Treycen knows she is in heaven but he does not understand why he can't go visit her, he just recently asked me if he could call his grandma Goold and I explained to him that she does not have a phone in heaven and he says to me, "Mom everyone has cell phones and I know she took hers with her"  he then goes on telling me he is going to go visit her, I again explain he can not go visit her until he gets very old, and he tells  me I know how to get there and I know how to get back, you just float down on a cloud? I asked him why he thinks that and he tells me that's what dogs do, it then clicks to me, he has been watching "All Dogs go to Heaven" he has such a sweet spirit, he misses her so much already and wishes he could just go visit her...