"Does Johnny have to go potty?" "Do you want some wa wa?"

Speaking to young children this way sounds sweet and motherly, but it may also slow down language development. A study published in Cognitive Psychology suggests that speaking in complex sentences to young children may set a better example and improve their language skills.

Janellen Huttenlocher, Ph.D., head of the developmental psychology program at the University of Chicago, observed 305 local children in 40 preschool classrooms. She found that children whose teachers used complex speech—sentences with multiple nouns, verbs or clauses—had higher language-comprehension skills.

In a separate study, Huttenlocher found that children whose mothers used more complex language were more likely to do so themselves. But parent/child studies cannot confirm that the way we speak to children affects their language skills because the results could be attributed to genetic or other factors.

Lisa Washington, head nursery and kindergarten teacher at the University of Chicago Laboratory Schools, agrees that baby talk is a hindrance: "Grown-ups feel they have to talk slowly or loudly or with a singsongy voice to kids." She says this doesn't challenge children to learn new language skills.

What may seem like common sense to preschool teachers has been a subject of hot debate by scientists. For years, many researchers assumed that language was programmed into the brain from birth, says Huttenlocher, because all babies have similar grammar patterns when they first start to speak. Linking language skills to environment, she says, "was a real scientific thrill."