Every parent knows how critical it is to have a sippy cup on hand, and three drinking vessels from a pair of ancient German graves reveal that such cups were just as important 3,000 years ago as they are today.

Across the European continent, archaeologists have dug up curious pint-sized pottery from sites dating back to the Neolithic Period, including small cups and bowls with drinking spouts. Left to ponder their purpose, some researchers have suggested the vessels were feeding cups for the old or infirm. Others theorized that they were used to feed ancient infants, even though our ancestors’ young relied on breastmilk.

A new study examined several Bronze and Iron Age cups unearthed from children’s graves in the 1990s to confirm the latter theory. By analyzing ancient residues left in the vessels, scientists believe that the cups dispensed animal milk used for what perhaps could be best described as feeding time in the prehistoric nursery.

“It was looking at the context of graves that really confirmed that they were infant feeding vessels,” says Julie Dunne, of the University of Bristol, co-author of the study published in Nature. “This is really the first direct evidence of what infants are not necessarily just weaned on, but I’d say fed as well. It’s quite likely that they were supplemented with this animal milk.”

Similar vessels shaped like animals found in the region suggest a second purpose. “The fact they made some of them to look like animals is to make their children smile, isn’t it?” Dunne says.

Rebecca Gowland, a Durham University bioarchaeologist not involved with the research, says the fact that an infant under six months old was being fed animal milk, and later died, poses interesting questions.

“Had the infant's mother died and was that why he/she wasn't being breastfed?” Gowland asks via e-mail. “Or was there another reason for not breastfeeding the infant? For those over six months, you would expect some form of supplementary food as the article suggests, but it's fascinating that the babies were buried with their drinking vessels.”

Fatty residues found in pots from across the northern Mediterranean suggest humans began consuming milk and dairy products from domesticated animals during the Neolithic revolution, at least 9,000 years ago. Soon after hunter-gatherers started to produce their own food through agriculture and domestication and settle in larger communities, they began using animal milk.

A study of milk proteins found in ancient plaque, released earlier this month, provided direct evidence that Neolithic adults consumed cattle, goat and/or sheep milk in Europe beginning at least 6,000 years ago. Genetic studies suggest Neolithic adults had lactose intolerance, so instead of drinking milk people may have processed it into digestion-friendly cheese or fermented it into yogurt.

Among the many changes during the Neolithic revolution was a prehistoric baby boom that led to overall population growth, evidenced by a marked increase in the proportions of infant and juvenile remains found in excavations of the time period. New feeding habits for children may have helped spark this population spike. To explore how ancient infants ate, studies have delved into ancient breastfeeding and weaning practices by analyzing bones and teeth—research that’s now supplemented by the direct evidence of milk in infant feeding vessels.

The cups Dunne and colleagues analyzed were found at a pair of sites in Bavaria, dating to 1200 to 800 and 800 to 450 B.C, but similar types of prehistoric sippy cups have been found at European sites dating back to 5500 to 4800 B.C. Could Neolithic European children also have drank animal milk from them as their Bronze Age counterparts did thousands of years later?

“In a later period, we now have positive evidence that these might be baby or toddler feeding vessels. So the next step is to go to examine the same types of vessels in earlier periods,” says Eva Rosenstock, an archaeologist at the Free University of Berlin unaffiliated with the research.

“There’s a really broad story here in feeding infants these sorts of foods,” Dunne says. “Hunter-gatherer mothers would have fed infants quite a different diet. They didn’t have milk from domesticated animals or cereals available to them.”

Hunter-gatherers also tended to breastfeed for several years and give birth less frequently. But once people settled down with domesticated animals, plants and supplementary food products, researchers theorize that the interval between births shortened dramatically and sparked a population explosion.

“Feeding children animal milk could have even been a motor of population increase by enabling shorter lactation periods for mothers,” says Rosenstock. “Once you had milk, you could feed your babies supplementary foods earlier, and maybe by doing so reduce your birth spacing and have more offspring.”

Like a spilled milk smell that can never quite be removed from a car, residues from these ancient milks, while imperceptible to the human eye, remained in the cups for thousands of years, which Dunne calls “very, very fortuitous.”

The reasons why can be seen at the microscopic level. “These pots are unglazed. If you were to put milk in the pot, the fat is absorbed into the very small pores and sits there very happily for thousands of years,” Dunne says. “These lipids are the perfect size to fit within the vesicles of that ceramic fabric. It is quite fantastic that they do survive.”

The scientists put the ancient fatty-acids though molecular and chemical isotope analysis and compared their signatures with those of known milks and animal fats. Though the analysis match couldn’t tell exactly which type of ruminant milk once filled these tiny children's cups, cattle, sheep and goat bones are found at settlement sites across prehistory.

Other farm-produced foods were also available. If it is possible to recover preserved proteins from the ancient vessels, Rosenstock says that a more complete picture would emerge of what the children ate—including whether cereals might have been mixed with the milk.

“Milk plus cereal is such a good combination,” she says. “Those mixtures have a very nice amino acid spectrum that’s very wholesome, and they’re a good supplemental or weaning food.”

The fact that milk residues can be detected at all in these cups after thousands of years, however, highlights a significant problem that Neolithic parents would have encountered: It would have been very hard for them to keep the cups clean.

"It is unlikely that these vessels were sterilized, so their use would not have been optimal for very young infants, as they were potentially a source of pathogens,” Gowland says. Exposure to diseases like gastroenteritis was a significant threat, and a diet of animal milk also fails to provide human babies with all the benefits of breastfeeding. Human breastmilk packs all the nutrients infants need, contains immune cells that protect the human body from infection, and builds the diverse gut microbiome that’s essential for good health.

The fates of the cups’ owners suggests that they weren’t in good health. But at this point, it is unclear if the practice of consuming animal milk, or perhaps not having access to breast milk, had anything to do with their early deaths.

“Sometimes in archaeology you do get this immediacy, and a connection, with the artifacts and therefore the people,” Dunne says. “And holding these you really can think of these mothers and their little babies, and how they buried them in these little graves and put their own little feeding vessels in with them. I think that’s telling us an awful lot about the love and the care that prehistoric moms would have spent on their babies.”