What age?
In late elementary school, my child enjoyed helping walk the dog and socialize the puppies through the dog rescue where we got our dog (K9 lifesavers). He also went to the soup kitchen with his Grandma and her church group.
For middle school, there's a group at the Zoo called "Zoo Crew" that's part of Roots and Shoots
http://www.rootsandshoots.org/. I also know kids this age who have made connections with nursing homes, visiting the elderly.