Start by asking the question, "What can we do to help the community?" The phrasing presumes it's not a matter of if the family will participate, but how. Bring the family together for a group discussion, then suggest several types of projects and ask for input. "Kids will be more invested if they feel like they have a say," says Jenny Friedman, author of The Busy Family's Guide to Volunteering (Robins Lane Press) and executive director of Doing Good Together, a group that aims to inspire families to volunteer.
If you're dealing with an independent teen, put him in the driver's seat by asking him to do some online research. For resistant teens, it's best not to insist on participation right away. Try easing them into it instead. For example, if your daughter likes to knit, say, "Wouldn't it be fun to make blankets for soldiers?" If your son is artistic, you could mention that one of his paintings could lift the spirits of a child with cancer. This may help them realize on their own that they have something special to offer.