It all adds up. On average, daycare in USA costs $18k a year per child ( https://www.care.com/c/how-much-does-child-care-cost/ ), which is the best measure of the total resources that it takes up, all-in. Median income for a 30yo man is $55k and for a woman $45k. So even with just two kids, the lower earning parent with the non-greedy job is not clearing much if anything over the cost of the daycare.