At NBC News' Education Nation Summit on Tuesday, Republican presidential candidate Mitt Romney said it was preferable for one parent stay home when kids are young. 

The comment came during a discussion of early childhood education and preparing children for kindergarten. "It's an advantage to have two parents, but to have one parent to stay closely connected and at home during those early years of education can be very very important," Romney said. 

Ann Romney was a stay-at-home mother to the couple's five sons. 

In 2011, 63.9 percent of the mothers with children under 6 years old held jobs outside the home, according to the Bureau of Labor Statistics. 

Romney also argued at the summit that teachers unions' contributions to Democrats were a conflict of interest that distorts negotiations.