Ametrine,
You are doing great.
I would take him to his favorite kid activity (bouncy place, kid's play, meery-go-round, etc..) and at night ask him how much fun he had. And tell him you had fun as a kid as well but you can't do it now because it would look weird. There are things that you can enjoy at the particular age and he should enjoy it. And being adult is not as easy and growing older also means carrying more responsibility. That's why god creates men to grow the rate that we are, etc...
I am not sure what I can tell about heaven. My DD said I have not been to one and I would not know what it is like. And she can't find what heaven looks like in youtube either :-)
