When my Grandmother passed in 2007 we simply told the kids the truth. they were 8,4 and 2. the 2 yr old didn't understand obviously (well he was 23 months) We told them GG had been sick (they already knew this) and that it was her time to die. We explained what happens when you die.. Like how your heart stops and without your heartbeating you no longer live ect ect.. then we said GG has gone to heaven. we explained how the body gets buried but the spirit goes to heaven..

just explain it how you think about it.. Like if you believe in heaven ect then just say that.. be open and honest and explain how when someone dies we can no longer see them like we see each other but we can remeber them in our heads. like a dream. remember all the fun times they had with that person..