My wife works at La Petite and unless it's different because it's at a business, it is 12 kids to 1 teacher...
We looked into maybe doing something like this a while back, the issue you will run into is insurance (AND YOU HAVE TO HAVE INSURANCE!!!) it's $$$$
Also, remember, a bunch of kids running through your house, you will get things broken unless you finish the basement or something and have them stay down there.