CHICAGO (AP) — Dr. T. Berry Brazelton, one of the world's most well-known pediatricians and child development experts whose work helped explain what makes kids tick, has died at age 99.

Brazelton died Tuesday at his Barnstable, Massachusetts home. The cause was congestive heart failure, said Stina Brazelton, his youngest daughter.

A Texas native long affiliated with Harvard University, the plain-spoken Brazelton was widely lauded for changing the understanding of how infants and children develop. The pediatrician, television personality and writer was still spry into his 90s, having published his memoir in 2013, shortly before his 95th birthday, and remained active teaching, researching and lecturing worldwide.

"Oh golly, I don't want to give up," he told National Public Radio in an interview aired on Father's Day 2013. "I learn every time I see a new baby, every time I talk to a new parent."

Parents knew Brazelton best from his popular Touchpoints books, along with the long-running cable TV show, "What Every Baby Knows," and his syndicated newspaper column, "Families Today." He also spent a half-century working as a pediatrician in Cambridge, Massachusetts. After retiring from that practice in 1995, Brazelton estimated he'd seen 25,000 patients.

Doctors knew Brazelton for his Neonatal Behavioral Assessment Scale, sometimes called the Brazelton scale, published in 1973. It is still used in hospitals and research to evaluate physical and neurological responses in newborn babies, and to assess emotional well-being and individual differences.

In 2000, he was named a Library of Congress Living Legend. He won a 2012 Presidential Citizens Medal, appearing beside President Barack Obama at a White House awards ceremony on March 11, 2013.

In an interview that year with Boston radio station WBUR, Brazelton offered his simple advice for frazzled new parents: "I'd like for them to learn that they can understand that baby by watching the baby's behavior."

Brazelton "showed the world that babies are individual people from the very beginning," said longtime colleague and friend Dr. Joshua Sparrow.

The first of Brazelton's more than 30 books was "Infants and Mothers," published in 1969 and translated into 18 languages. The title of his memoir, "Learning to Listen," described his philosophy for understanding infants.

Brazelton believed that moments he called "touchpoints" helped define childhood, reflecting periods when children's behavior seems to fall apart that signal an impending advance in development.

From crying outbursts when learning to walk to the temper tantrums of the terrible 2s to kindergartners' nightmares, Brazelton's thoughtful descriptions of "touchpoints" helped parents make sense out of these vexing moments.

His approach was influenced by Dr. Benjamin Spock, America's first widely-read baby doctor who empowered parents to make their own decisions and respected children as individuals.

"Rather than compete, I always felt like I added the concept of looking at the child, finding out what the child is trying to tell you and let them lead you," Brazelton said.

Stina Brazelton said as a parent, she read Spock — not her father's books — and didn't seek his advice until she learned that her son's doctors were heavily influenced by her dad. She said one of her father's lasting legacies is his encouraging other fathers to express their feelings for babies and young children and to be involved in their development.

Born in Waco, Texas, on May 10, 1918, Thomas Berry Brazelton grew up with his businessman father and civic-leader mother who established what was likely the first abortion clinic in Texas in the early 1940s.

Brazelton began his lifelong study of children when he was just a boy. Brazelton felt his mother favored his younger brother Chuck. But then his grandmother put him in charge of babysitting young cousins.

"So I had to learn how to get inside of each of these children's brains to keep control ... and it was wonderful to learn to watch their behavior," Brazelton told The Associated Press in a 2006 interview. "I thought, well at least I can take care of other children."

His book publicist liked to say "Brazelton" rhymed with "razzle dazzle," but that was not his style. Despite a well-to-do upbringing and an Ivy League education, Brazelton was down-to-earth, and his low-key charm helped him easily connect with families from all walks of life.

Brazelton spent his undergraduate years at Princeton, earned his medical degree at Columbia and did postgraduate medical work at Harvard, where he later taught and was professor emeritus.

He founded the child development unit at the Harvard-affiliated Children's Hospital Boston in 1972. He also created two programs there: The Brazelton Institute, which trains professionals in using Brazelton's newborn assessment scale; and the Brazelton Touchpoints Center, which helps educators and social service agencies better serve families of infants and young children.

Dozens of sites nationwide have used the Touchpoints approach in helping parents raise healthy children, including programs on several American Indian reservations.

Sparrow said Brazelton told him several days before his death that he wanted to make a trip to Boston before a big birthday celebration planned there. Brazelton would have turned 100 on May 10.

"We will still have that party, and celebrate his life and celebrate his work," Sparrow said.

Brazelton's wife, Christina, died in 2015. He is survived by three daughters, a son and five grandchildren.

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Follow AP Medical Writer Lindsey Tanner on Twitter at @LindseyTanner. Her work can be found here .