Is your lawn plagued with pesky dandelions? You could do what my dad did when we were growing up and pay your children to pick them. It solved a problem for him and gave us something fun and profitable to do during the summer!
My dad started out paying us a penny per dandelion, but after the first year, our zeal for the task increased and he had to lower the wage to 1/2 a penny per dandelion to keep us from running off with a fortune! (We had discovered that if you dig deep enough down into the dandelion plant, you can find dozens and dozens of buds at the base waiting to spring up- you can imagine what a goldmine we thought we had found once we made the discovery :-)
Have you come up with paid tasks that you find work well for both you and your children? I'd love to hear about them!