I don't know what the regs are... so take what I am saying with a grain of salt.

I think that catering to one age group would be a good thing in many ways. The set up would be ideal for that age group, activities, meals, etc etc. I know many centres and home daycares (here) won't accept children until they are 18 months. So parents need something until that age, kwim?

If you are limited by age how many children you can have, then I would revisit the notion of catering to an age and instead cater to a philosophy (ie: what you think is important in childcare, play through learning, etc etc).

Good luck!