Reading all your comments I can understand where you are all coming from. My DS1 died the day after his 5th birthday and DS2 was 3 just 2 weeks later. He worshiped his big brother, he was his shadow.
It was awful, trying to explain to DS2 that his brother could never come back was sooo hard.
Painting a picture of this wonderful heavenly place, where children no longer suffer and can play freely forever without pain just lead to DS2 asking 'why can't we go and see him' 'why doesn't he visit me' 'why did he go without me' 'didn't he love me anymore'.
DS2 pictured heaven as a place that was just a bus ride away and started to blame himself because his brother went there and he's not allowed to go. He started to say he wanted to die so he could be with him again. He got horribly mixed up and his confusion turned to anger and aggression.
This affected him at nursery and school and with the help of councelling, child pyschologists and SENCO teams he has eventually learned to deal with it. DS2 is 6 now.
The main lesson I was taught early on in the councelling (which was for me too)was that when a young child asks what happens when you die, you give them straight forward, truthful answers. Try not to glorify 'heaven' as a wonderful place. Be frankly honest. We don't know. We have never been there. You will never really know until you die. As hard and blunt as it seemed, that helped DS2. When he asks 'where is heaven?' we answer 'I don't know'. He still looks to the sky and blows kisses to heaven, he's accepted that it's out there somewhere and his brothers there and when he's sad, he talks to him. I often hear DS2 say his name in his sleep. I often hear him chuntering away to his photograph, he has developed his own understanding and has come to terms with it, although it took time and heaps of heartache. He also has a small collection of DS1's favourite things that he can get out whenever he wants to, like a memory box. He knows he can talk about him whenever he wants to with me and ask to watch videos of him or look at the photo albums. I forced myself to do this from an early stage in my grief, the first time I couldn't see for my tears, now we can sit together and look, laughing and remembering. It's took years of hard work to get to this stage, but DS2 can cope with it now and doesn't get angry everytime he thinks of his brother going away. He'll still have a quiet moment and say 'I miss .... mummy, I wish he could come back' and calmly glance at the sky, then carries on with what he was doing.
Just be honest. Although it seems hard and blunt, it prevents impossible to answer questions, confusion and heartache.
My thoughts are with anyone who has to explain the death of a loved one to a child.