If there is a heaven, I believe in Universal salvation (hence, once of the reasons I'm a Unitarian Universalist). However, what I tell my children is that I'm not sure what heaven is like, or if there is a physical heaven. I also tell them that the one thing I'm sure of is that we give of positive and negative energy in our life. After we die, when people think of us and smile, the positive energy we gave is being remembered and that is a kind of heaven. This also applies to positively effecting someone's life and they in turn are able to help others.
I'm not sure if I explained that very well. We also emphasize that they should make up their own minds about god and heaven.