Help at a school
If you have some spare time, you could offer your help to a local primary school. Schools are often keen for extra help - it makes students pay more attention if they have an outside visitor, and allows the students to have more direct attention.
You will need to contact the head teacher of the school to ask their permission. Make use of any contacts you have - maybe go back and visit your old primary school. You may need a police check to prove you do not have any criminal convictions.
Suggested ways you could help:
Listen to younger children read
Run an after-school club (e.g. sport, drama, debating, computer studies)
Give a talk about something interesting you have done, a place you have visited, or an issue you are interested in
Offer to accompany a class on a school trip
Help out with a school play (make props, help at rehearsals, sell tickets)