I've done a lot of volunteer work with my kids. Times are tough and food is very expensive right now, so helping collect food for a local food cupboard is a good project. We've collected from neighbors, family and friends, and brought the food to a local church food cupboard. We've also made meals at home and packaged for Aid to Friends and Meals on Wheels.
You can also do some other projects right in your neighborhood that are completely informal, such as walking along the street and picking up trash, perhaps planting flowers or doing yard work for an elderly neighbor. What's nice about things like that is kids will develop a sense of seeking out opportunities to be helpful to others. We used to do that sort of thing when my boys were very small. Then one day I was walking with them to school when they were in 8th and 6th grade. I just went with them that day to enjoy the weather and stretch my legs. Usually they walked to and from school without me. I noticed that they picked up trash here and there along the way, and at two houses they moved the newspaper from the end of the driveway to the front door. I asked why they moved the newspaper, and they said that they noticed that older people lived there and had a hard time walking to get the paper in the morning. One day they asked the ladies who lived in the houses if they wanted them to bring the paper up to their door every day, and so they did. I was very proud of them for identifying a need and helping out.
Have fun! I think you're doing a wonderful thing.