It hasn't been scientifically proven, but I'd bet my breast pump that it has to do with babies' potent sense of smell. Newborns are masters of odor detection, and crying out when a delicious pot roast hits the table might be their way of responding to such a strange new aroma -- or one that they know means you're busy.
Compared with little kids, adults hardly notice the more subtle scents around them. The sense of smell develops much earlier than vision but declines on the road to adulthood, so a child experiences much more of life through her nose than her parents do. What's going on in there:
In the Womb: First Smells
Even before they're born, babies can detect odors -- the coffee you made for breakfast, the exhaust on the freeway on the way to the hospital. They start to use their nose when you're about six months pregnant (before then, fetuses have a temporary plug of tissue in the nasal cavities that eventually dissolves).
How do we know? Studies with preterm infants born after just 30 weeks of pregnancy have shown that they respond to certain scents, so it's believed that fetuses of the same age are capable of the sense too. Many things a pregnant woman eats or smells somehow make their way into her baby's watery world, and because the olfactory system, like the rest of a child's brain, is sensitive to early experience, those odors probably influence a baby's later ability to detect scents. All this before he takes his first whiff of the world.
Lise Eliot, Ph.D., is an assistant professor of neuroscience at the Chicago Medical School and author of What's Going On in There? How the Brain and Mind Develop in the First Five Years of Life.
Babies: Hardworking Little NosesThere's growing evidence that a newborn's sense of smell helps her adapt to life outside the womb. She can detect and discriminate between all kinds of different odors, judging by her dramatic facial expressions or sudden alertness when presented with an aroma (like the dinner you foolishly thought you were going to sit down to enjoy).
Plus, a lot of a baby's early knowledge is based on what she can smell. Research shows that newborns can distinguish their own amniotic scent from others', and babies just a few days old can perceive their mother's breast or underarm odor, sometimes from several feet away.
As time goes on, babies can recognize Dad by smell too, but generally speaking, mothers have the advantage in this department. As a mom, you're literally dripping with many of the same smells that your baby became so fond of in her recent amniotic home. Familiar cues are present in all of your bodily fluids -- sweat, saliva, colostrum, breast milk, and, especially, the rich secretions of the glands that lubricate your nipples and areola -- which is why, given a choice, infants prefer to nurse on their mother's unwashed breast.
You can take advantage of your baby's impressive sense of smell and unabashed preference for familiar odors. The next time she's having trouble falling asleep, tie your unwashed T-shirt or burp rag to a bar on her crib (away from her face) to see whether it helps her soothe herself back to dreamland. And you needn't feel like you should be washing her pacifier every time it drops out of her mouth; the smell of leftover saliva is probably part of what makes it calming for her.
Kids: Understanding OdorsSmell can comfort past the baby years too. The unique odor of your toddler's lovey is a major reason it's so soothing. And it's why he gets so upset when you try to wash it.
It isn't until the early preschool years, though, that children realize that they're using their nose to explore an odor coming from a specific object. By the time they're 4, most kids are sniffing practically every flower they come upon, sticking their nose into a loaf of freshly baked bread, or nuzzling deep into Mom's or Dad's neck when they're picked up at daycare.
They may also seem especially interested in smells because they're finally able to label them with their rapidly growing vocabulary. Should I make the mistake of baking a batch of cookies or muffins without telling my 4-year-old, Sammy, he'll rush into the kitchen, exclaiming, "What's that good smell?" (Of course, that's usually followed by "Why didn't you let me help?")
There are plenty of odors a lot less pleasant than chocolate-chip cookies, but young kids don't get too distressed by them. The ability to distinguish fine from foul odors may not develop until they're about 3 years old. In one study, researchers found that toddlers barely looked up when a nasty odor (like rotten eggs) was secretly introduced into their play area.
When they do start to figure out various smells, you'll probably hear about it. Preschoolers enjoy making themselves useful by pointing out when the baby's diaper needs changing, when the garbage is ready to go out, when the milk's going bad, and on and on. You can encourage your child's understanding of odors by talking about them ("Doesn't the grass smell great right after we cut it?") or playing games (such as those below).