A LOT depends on what you plan to do IMO. As a provider - as the babies get older - will you be doing any crafts/lessons, etc? Also, IMO you can charge more by offering to provide all food (and making it nutritious food and not PB&J all day every day) - since working parents consider that a huge benefit. My kids have been in an in-her-home provider since 3 mos old - and she is WONDERFUL - they came home from her house having learned to write their names at 2 and 3 years old - they always have birthday/mother's day/etc. 'cards' and crafts made for us. They read a lot and significantly limit TV time. They play outside a lot when able. These things are HUGE to a working parent. We had to use a part-time substitute for her for awhile, we paid the same price, but got PB&J only all the time - plus cookies every afternoon and the TV on all day long.....Will you be willing to drive to preschool programs eventually? That is another big benefit.
I think people will pay premium for a 'top quality' provider. Mine happens to be pretty cheap - but I would pay more for her. I pay $25 a day per child and I send them 3 times a week. She provides food - more often than not - hot meals plus fruits and veggies.
Don't forget the negatives of having someone do it at their house - no backups - anytime my sitter's own daughter is really sick or needs to go to an appointment, etc. - we get last minute notification that she can't take them. Luckily, this is rare, but it is something that needs to be offset.
Also a consideration - will you be claiming it? If the parents can't put your SS# on their forms, they won't get the tax write-off, so that should make it cheaper too. Daycare centers would be deductible and eligible for flexible spending accounts.