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Your Baby's Fussy Behavior Could Actually Be A Very Good Sign

Watching your baby learn and develop is fascinating, but you probably always want to know more about what's going on in that busy brain. If you're heard about a mental leap in babies, this concept could explain a lot about your kid's behavior (read: likelihood of being fussy) and growth.

Generally, mental leaps are explained as a rapid change in your baby's mental development. "With every mental leap your baby makes, they gain a new perceptive ability. That new ability enables them to perceive, see, hear, taste, smell, and feel many new things that your baby was unable to perceive before," Xaviera Plas-Plooij, co-author of The Wonder Weeks! A Stress-Free Guide To Your Baby's Behavior, tells Romper via email.

There's also an easy way to explain the concept to tech-savvy people. "One of our readers compared a leap to an update on your laptop or phone: it happens all of a sudden and you have no control over it, but then afterward your phone can do many new things," explains Plas-Plooij. To your baby, however, this sudden "update" can be overwhelming or frustrating. The change may be accompanied by a fussy phase, which could mean more crying, crankiness, and clingy behavior than usual. However, this change in behavior is simply the way your baby is reacting to their newly "upgraded" brain and its abilities.


The idea of mental leaps was explained in the 1992 book The Wonder Weeks by anthropologist Hetty van de Rijt and psychologist Frans Plooij. Since that time, the idea has given rise to several additional books, as well as the The Wonder Weeks app, which is designed to help parents keep track of these major mental changes in real-time. The publication of subsequent books, as well as the website and app, are now overseen by the original authors' daughter, Xaviera Plas-Plooij. Now a multimedia experience, the ideas behind The Wonder Weeks have found some support from child care experts. "van de Rijt and Plooij not only have they explained the periods of puzzling, difficult behavior in infancy which so worry parents, they have also shown how these behaviors mark developmental leaps," said John Richer, Ph.D., the consultant clinical psychologist and Head of Pediatric Psychology at John Radcliffe Hospital. "What’s more, van de Rijt and Plooij have described the play and communication that work best with babies at different ages and thus helped parents understand and connect sensitively with their babies." For some people in the child care world, the idea of mental leaps just makes sense and explains so much about a baby's behavior.

However, it's important to know that the idea of babies experiencing mental leaps is worth considering as part of a larger picture of development. The book and app can be seen as a resource, but not a definitive guide to all child development (which it never claims to be, anyway). "From what I was able to find out, there is not a consensus on [mental leaps]. AAP does not have policy that addresses it," Lisa Black, Media Relations Manager for the American Academy of Pediatrics, tells Romper via email. At least one physician also recommends using the mental leap idea with some caveats. "What I love about 'The Wonder Weeks' is how it can give new parents confidence in navigating the development of their baby," wrote Annie W. Kerr, MD, FAAP in the blog for Texas Children's Hospital. However, Dr. Kerr cautions parents not to overlook signs of potential illness just because a baby is going through an assigned "fussy" week. "I also try to constantly remind parents that infant development progresses on a continuum; each individual baby will develop skills according to his or her own unique timeline," said Dr. Kerr. As with just about everything else related to parenting, your mileage may vary.

However, if mental leaps do occur as described in The Wonder Weeks, then they could be a potentially major experience for the baby. "All of a sudden, there it is: a new mental ability. And the only one to notice is your baby," says Plas-Plooij. "Their brain is suddenly able to perceive new things. Almost nothing is as it was before." In this case, it's no wonder mental leaps may lead to fussiness, and a baby who needs a little extra TLC from their parent at the moment, but once parent and baby have a moment to adjust to the new "features," the possibilities will seem endless.


Xaviera Plas-Plooij, CEO of The Wonder Weeks! and co-author of The Wonder Weeks: A Stress-Free Guide To Your Baby's Behavior (6th Edition).