Baby-Sitter Robots and Population Growth Robots and other machines may someday transform child care without eliminating the human touch. As any parent can attest, caring for young children is time-intensive. As a result, child care is one of the largest segments of the economy, at least when the nonmarket household sector is included. Many parents treasure their children and feel the benefits outweigh the time and costs of having children. Many other adults decide not to have their own children, and the time costs are sometimes a factor in that decision. To be sure, the influences are complex; a study by Satoshi Kanazawa of the London School of Economics, which suggests that women with higher IQs are less likely to have children, made waves in the blogosphere in recent days. The time costs of child care are also a factor limiting teenage pregnancy. Teenagers are encouraged to complete high school and higher levels of schooling, and students" parents, teachers and counselors - if not the teenagers themselves - understand that teenage motherhood takes time away from schoolwork and thereby makes academic success less likely. The world would be very different if children did not need so much time. More people, perhaps especially teenagers, would have children if children did not require so much time and attention, especially from their mothers. People who already have children despite the cost might have more of them if they expected each child to require less time. As the time costs of children limit population growth, the population would be likely to grow more rapidly if those costs were somehow reduced, whether you think that such growth is a good thing or a bad one. If each child required less parental time, you might expect parents - especially mothers - to use their time on other things, like work more outside the home, pursue their own schooling or leisure activities. But it is possible that people would spend more of their lives caring for children and less time on those other things because they would be having more children. Wealthy people have already had some of these opportunities, because they can afford numerous baby sitters, nurses and tutors. But technological progress may one day reduce child-care costs for the general population. Because robots and other machines take on a number of tasks formerly done by people - even playing chess - and are expected to do others like drive cars, perhaps we should expect that robots will some day take care of children, too. People today may believe that it would be inhuman or immoral to leave young children at home alone with a robot or to drop them off at a day care center staffed by machines. But economic and technological changes of the past have already transformed child-rearing attitudes and practices: take test tube babies, working mothers, screen time, fast food or children with their own telephones. There is little need to worry that machines will take over all aspects of child rearing. People will always have a comparative advantage over machines, even if machines could in principle be better at just about anything. For the same economic reason that the world can produce more by assigning some tasks to unskilled people and other tasks to talented people, people will be doing tasks that are difficult for machines relative to other tasks. But perhaps robots will make parenting easier and thus more popular.