i would do regular volunteer in your community. things like once a month. lots of resources around that you can look at in your community to see what you can do. food banks. local farms. non profits. of course the homeless people.
i think that is attainable.
do you not already volunteer? or are you trying to volunteer to set up an example for your 7 year old. i think that's a wrong way of looking at things. find out what you are passionate about and then include your child in it. what should be key is your need to volunteer in what YOU find interesting. like SPCA. you can help with cleaning out cages and take ur child along to help. or perhaps you enjoy gardening. maybe you could become involved with the Native Plant Association in your area and help them gather seeds and clean and store them properly.
there are LOTS of volunteer opportunities for kids abroad. TONS. if you have the money. instead of habitat for humanity i would do something like http://www.globeaware.org/thailand-volunteer-vacations-voluntourism-environmental-work-and-working-vacations
i know a 7 year old who went on this volunteer mission and it changed her life.
these books come with all the details for you to choose from.