If you have one half-hour per week or up to a 2-hour session once a month you could volunteer in the Library. There are jobs ranging from reshelving books and putting pockets and labels in new books to covering paper jackets with plastic covers, as well as checking for overdue books and sending out notices regarding this.
Hours are flexible so you can work around your other activities and fulfill your volunteer obligations.
Volunteering in the library is a great way to see the wonderful resources available for your children of all ages. Remember parents may borrow books too.