It's a fairly easy concept for kids to understand that you need money to buy things in life and that you need to work to make the money you need. Share what you do for work with your children; if possible, take them to your workplace so they can picture where Mommy, Daddy, or both go during the day. When work interferes with your time with your kids, be open about that (i.e. "I won't be home when you get off the bus today because I'll be working").