The vocal patterns parents everywhere tend to adopt during exchanges with infants and toddlers are marked by a higher-pitched tone, simplified grammar, and engaged, exaggerated enthusiasm. Though this talk is cloying to adult observers, babies can’t get enough of it. Not only that: One study showed that infants exposed to this interactive, emotionally responsive speech style at 11 months and 14 months knew twice as many words at age 2 as ones who weren’t exposed to it,” she writes.