It's 12 kids max. There have been ratio problems in the past, as people weren't paying attention to the difference between under 2s and 2-3-year-olds. Also, people forgot that brought-along siblings count towards ratios.
So, as long as the 12 kids were all over 2, and as long as no additional siblings were brought along, we were fine (I think?) with one professional and two parents. (But we do generally have kids under 2, and we often have brought-along babies, belonging to a working parent.)
We are talking about moving to two professionals and two parents per shift, anyway, as numbers go up. (Or maybe two professionals and three parents, as time goes on?)
The ratios thing is funny - I find it weird that the same ratio applies for professionals and amateurs, so to speak, and for inside an Ofstead-checked nursery, and out on the street. In Canada, the ratio for under-5s (I think?) is 1 to 5. Certainly that's the lowest ratio they have.