How come motherhood isn't considered a full-time job?

So I'm a college kid that works part-time as a day care worker. I have four babies at once so it's pretty hectic and very difficult. However, even if I only had one baby it would be a full time job. How come women that stay home with their babies aren't considered to be working? Our society devalues motherhood and doesn't place any importance on the interactions between the baby and the caretaker. I mean, my day care place will hire anyone as long as they don't have any sex crime convictions. People constantly quit and new ones are constantly hired. Is it weird that so many career women trust me alone in a room with their babies all day? What if I'm nuts?? Or stupid and drop one of their babies?