Whatever your children's age, they deserve honest answers and explanations. It's what strengthens our children's ability to trust. Also, when we don't provide a straight forward answer, kids make up their own fantasy explanations, which can be more frightening than any real, honest response we can offer.
While we may not want or need to share all the details of a particular situation or issue with our child, try not to leave any big gaps either. When we do, children tend to fill in the blanks themselves, which can generate a good deal of confusion and concern.