Developmental milestones help us understand when a child needs help, but meeting them early doesn’t necessarily predict long-term success
This piece is part of Scientific American’s column The Science of Parenting.
By Chris Sheldrick, PhD, 6th May 2024
For about 24 hours around a decade ago, I was in a panic. My son was about eight months old and had just begun to crawl. This is common for children his age, but the way he crawled looked unusual to me—he scootched along on his belly, kind of like a soldier crawling under barbed wire. I soon learned that my impression wasn’t far off—I looked at the scientific literature and found that people call this “commando crawling.” I also learned that it is incredibly common among people with achondroplasia, a severe growth disorder that leads to short stature, which spurred my daylong panic.
One study of children with achondroplasia found that 100 percent of them commando crawled when they first started crawling. As a parent, I didn’t know what to think. I felt more than a little scared, and I had no idea what to do. Developmental milestones, like crawling, seemed so straightforward—but only as long as my son was passing them.
Did my son absolutely have achondroplasia? Science couldn’t definitively answer all my questions, but it offered some answers about developmental milestones. Simply put, these markers help us to compare our child’s development to others of the same age. On the plus side, this can help us identify problems early enough to help. But there are drawbacks, too. Developmental milestones do not support definitive predictions, so they need to be interpreted carefully.
First I began to think through how well commando crawling might predict achondroplasia. Fewer than one in 20,000 children have this disorder. Let’s assume that all of them commando crawl. I asked myself: How many of those other 19,999 children also commando crawl? If it’s even as few as four, then among children who commando crawl, only 20 percent will have achondroplasia. As I learned, milestones do not support definitive predictions.
Finally I did the obvious thing: I talked to my pediatrician—a course of action with no real risk and with potential for significant benefit. And fortunately, she was quite astute. As I watched her work, I imagined her wondering whether my son was the one in five with achondroplasia or among the other four who just commando crawled. She looked carefully at my son. Then she turned and gave me a long look. “Do a lot of people in your family have big heads?” she asked.
“Yes,” I admitted, “my son and I come from a whole family of people with big heads.” (Here I welcome readers to supply a punchline, if they wish.) As it turns out, large craniums are heavy and can make normal crawling difficult. This insight suggested that my son might be among the four (which it turned out he was). Thankfully our pediatrician knew how to interpret developmental milestones carefully.
If you are the parent of a young child, you likely have your own experiences with developmental milestones. You probably hear questions like, “Is your little one crawling yet? Walking? Talking? Drawing?” If you think your child is developing well, questions like these can be reassuring. But sometimes they can cause intense anxiety.
How do you know if there is cause for concern? Information is readily available, for example through the Center for Disease Control’s website or your local pediatrician. But it is also important to understand the science behind developmental milestones.
Read the full article in Scientific American