Work out where the kids go every day after school and ask for permission to post some good, professional notices on their boards. Add a little plastic pocket with business cards in it for people to take away.
Ballet schools, swimming pools, leisure centres, village halls, Scout huts, church halls, community centres ...
Mention all the important things that reassure parents - CRB checked, references available, experience. I would be happiest responding to an ad that gave a landline number, not just a mobile, but you may not want to do that.
Just my thoughts - mainly pinched from the endless hours spent reading notice boards whilst waiting for my kids to come out of many of the aforementioned!