Emily Oster, an economist at the University of Chicago and the mother of Penelope, 2, told me that the baby business is “a classic example of a perfectly competitive industry.” Nearly every product we buy — from coffee and cereal to hotel rooms and cars — is a commodity dressed up in premium packaging, Oster pointed out. But with baby products, the process is intensified. Kellogg’s, Ford and Starbucks can spend years tempting a consumer, but baby companies have a short window — often just the few weeks before a due date — to capture expecting parents’ attention. These campaigns often try to simultaneously scare and reassure. One dominant marketing strategy is to list all the features a product has (and, by implication, the competitors don’t) that will guarantee a healthy and happy a child. My favorite is the ubiquitous announcement that a product is phthalate-free because 1.) most people don’t know what phthalates are; and 2.) U.S. law regulates the use of phthalates — a plastic softener associated with birth defects in rats — in certain children’s products. (That said, I was reassured that my son’s sippy cup has no phthalates whatsoever.)

It’s easy to feel like a sucker once you realize that nearly every dollar you’ve paid over the commodity price is probably wasted. But the process also has enormous benefits for all consumers. Occasionally companies seeking differentiation come up with safety features that are eventually adopted by government regulation and mandated for all competitors. The National Highway Traffic Safety Administration, for instance, has been testing Safety 1st’s Air Protect+ system, along with other car seats that claim to offer special protection from side-impact crashes. If a particular company’s safety technology proves effective, eventually every car-seat maker will be required to include it, and side-impact protection will go from a premium feature to part of the basic commodity.

Benefits that we receive without paying extra are called the consumer surplus, and we see them everywhere in our economy. In the computer, generic-medicine and auto industries, in particular, today’s low-end bargain product has features (like fast processors, heartburn relief and air bags) that were considered luxuries not long ago. The child-products industry has benefited perhaps more than any other. In 1900, an estimated 20 to 30 percent of urban American children died before age 4. In 2010, less than 1 percent did. The early changes — penicillin, washing hands — made the biggest difference, but these days, competitive baby-product makers and regulators scour emergency-room records to identify every potential improvement. Now products that kill two or three children a year, like cribs with movable sides, are banned.

It might shock the shoppers at Brooklyn Baby Expo, but the idea that everything children touch should be completely safe is a fairly new one. In previous generations — and for most people currently living in poorer countries — having children was an economic investment. Viviana Zelizer, a Princeton sociologist, in her 1985 classic, “Pricing the Priceless Child,” tracked how childhood in America was transformed between the 1880s and the 1930s. During this period, Zelizer says, parents stopped seeing their children as economic actors who were expected to contribute to household finances. Families used to routinely take out life insurance plans on their children to make up for lost wages in the not unlikely event of a child’s death.