In 2013 Esposito and collaborators published a paper, when for the first time, scientists demonstrate that the babies calming response to carrying is an evolutionary trait of mother-child relationship.
They demonstrate that infants under 6 months of age, when carried by a walking mother, immediately stopped crying and show a rapid heart rate decrease. A similar behavior was evident also in mice mothers and their pups.
The calming response is regulated by central, motor and cardiac signals.
To conclude: mother, if your babies are crying, carry them, maybe pacing the floor and walk a little. This will help out little cubs calm down.
For further information: “Infant calming response during maternal carrying in human and mice”, Esposito et al., Current Biology 23, 739-745, 2013. https://doi.org/10.1016/j.cub.2013.03.041