One other thought - Vista Print and other similar company's have some great and inexpensive ways to advertise.

Get a magnetic door magnet printed up with your day care name and contact information and park it near the school - "BEFORE AND AFTER SCHOOL PLACES AVAIL. CALL 123-123-1234" Something like that.

If your house is on the main route to school, get a lawn sign with the same. They are just like corregated cardboard and you buy a H-shaped metal frame for a couple of bucks extra and just press into your lawn. Parents will see it then as they drive by.

Business cards too - always good to slip under the wipers of cars if there's an event at the school and place flyers on the community mail boxes if you have them too.

Do you have a little local publications. There's one in my community which goes out quarterly I think. A small business card sized ad in there is quite cheap. I've done that once before but for me, that's timing based.

Just some other ideas.