Do you get lots of calls for kids under age 2? I wouldn't expect a sudden rush of families signing up if you put the age group down just a few months. Not sure what area you are in but here most families begin care when their child is about 10-12months old (depending when their mat leave ends). I don't think there would be a huge increase in children aged 18months over age 24 months as in theory the 18 month olds have been in care for 6 months already.

I would say there is a fair bit of 'gear' needed for the younger age group that you would need to have and I would not really go out and buy all that on the hopes you get a family signing on, especially if it isn't really your 'dream' age group to work with.

As mentioned above put your energy into figuring out why you aren't getting families signed on and see if you can tweak things. Every thing from your advertising, initial email and phone contact and first in person meeting has a HUGE bearing on whether families sign up. Odds are you can adjust things to draw in the families you wish to have sign on.