It's always good to do service for the less fortunate, and a fun twist is a service trip!
Many kids and teens want to go on service trips, but they can be very expensive. If it's a first trip, have them do one within the country. These tend to be cheaper and are closer to home. If they want to do one overseas, I would recommend letting them. Seeing the world is important and fun, especially if they can improve the world in the process. Service trips are often upwards of $4,000 a person, so have your child fundraise at least half of the cost. If a kid is not emotionally stable enough, you might want to consider a family service trip.
Many organizations offer family service trips where the whole family can travel overseas and go sightseeing, shopping, hiking, etc. Doing service projects as a family is always fun and this is a great binding experience and a good time to teach your kids to be selfless. These trips can be very expensive though, so plan several years in advance so you can save for it.