What are you putting as your catch line? I think when people see simply "Daycare space available" then they call. I have found through my own experience that when you put 2 spaces available then they are thinking "why"

Or if you put a time line like 2 Spaces available for Sept then people that might be looking to start in Oct won't call.

It also depends where your ad is, the best time to post a new ad or top up is Thursday night or Friday morning as most people reserve there search for weekends.

Have you looked closely at your direct competition have there ads been there a while too? How do your pictures compare to others etc..you need to have your pictures show a day in the life at "your" daycare!