“Oh, we used to watch our first child like that,” a neighbor once said to me, as I tried to prevent my 2-year-old from swinging too high in our back yard. With her third child, though, she explained, “we just try to make sure she isn’t licking the driveway.”

The disparity between the way we treat our oldest and our youngest is a source of regret for many parents. We forgot to make the baby books. We don’t have as many pictures. We can’t even remember the youngest one’s first word. And where is that kid, anyway?

Now a new study out from the Journal of Human Resources will only make many of us feel guiltier. It turns out that first-born children not only have better academic outcomes, but that the differences in cognitive abilities for these children are evident as early as age 1 — and often stay that way, report researchers from the University of Edinburgh and the University of Sydney.

They write, “Mothers take more risks during pregnancy and are less likely to breastfeed and to provide cognitive stimulation for latter-born children.”

The research on the effects of birth order have been evident for some time. For instance, according to a 2013 paper from the National Bureau of Economic Research, “On average, mothers with two children were almost 8 percent less likely to say that their second child was one of the best in his class.”

The researchers, V. Joseph Hotz of Duke University and Juan Pantano of Washington University, found that “earlier-born children also had higher scores on the Peabody Individual Achievement Test and the Peabody Picture Vocabulary Test at age 10.”

According to the same study, moms also say that, when it comes to earlier-born kids, they’re more likely to “increase the supervision of one of their children in the event that child brought home a worse-than-expected report card.”

By the time you get to the second or third child, let alone fourth or fifth, who has time for more supervision?

Earlier-born siblings are more likely to be “subject to rules about TV watching.” Katie, a mother of three in Washington, is typical. “My 7-year-old didn’t watch much television at all until she was 2. And then the only things she saw were ‘Sesame Street’ and ‘Thomas the Tank Engine.’?”

Her 4-year-old and 3-year-old watch Disney Junior, Sprout and Nick Jr. They get to watch a show in the morning while the family gets ready to leave the house. They watch while their mother is making dinner and if she has to make a conference call for work.

The reasons for this difference are obvious. Parents have limited resources, and the more children we have, the less often any of them can get our undivided attention.

But there are other reasons, too. We’ve done this before. And we know an extra cookie here or there isn’t going to kill anyone and neither is an extra cartoon. We know that every sneeze doesn’t require a trip to the doctor. We know that 4-year-olds left alone for five minutes won’t stick a fork into a socket or swallow a marble. (Probably.)

Maybe it’s true that older kids get cognitive advantages, but younger kids have other ones. In an era of helicopter parenting, they get a little breathing room. They learn some independence.

They also learn to get along with other kids at home and may not have as much trouble negotiating relationships in school. When my oldest was in preschool, I had to stop playdates with only children. Whenever it was time to share, they screamed bloody murder.

Younger siblings don’t have to be taught they’re not the center of the universe.

In an era when fewer of us have neighbors available to go out and play, younger siblings have built-in playmates at home from the moment they’re born. Indeed, rather than using screens to deal with more children, we might do more to encourage them to play with each other without constant adult participation.

The head of a preschool once told me that parents often confessed to her they’re worried that if they have more kids, they won’t have enough of themselves to go around. She reassures them by saying the younger children “will have more people to love them.”

So maybe we can give ourselves a break.

Naomi Schaefer Riley is a senior fellow at the Independent Women’s Forum.