Parents often worry whether their child is growing and developing at the right pace.
Each child has their own timetable, but there are some milestones doctors look for.
Josie Reed is an energetic 4-year-old who loves Elmo, Peppa the Pig, and Elsa.
Whenever Josie comes for a check-up, Dr. Judy Larkin of Nemours duPont Pediatrics checks her physical and behavioral progress.
"There's a lot that we can tell by just watching them," Larkin said. "There are things that we can pick up early, that we can get kids extra help."
At two months, infants become more aware of their surroundings, and begin interacting with mom and dad.
"They might be smiling at them, they're responding to sounds," Larkin said.
At about six months, they've mastered rolling over, and are working on sitting without support.
They're also starting to babble.
"She started to babble early on, and just a lot of, like, really loud noises," Jennifer Reed said of Josie.
By 1, babies can usually say "mama" or "dada," and wave hello or goodbye.
They're also usually on the verge of, or have started, walking.
"She just kind of flipped the switch, and then was just full steam ahead and then I couldn't stop her," Jennifer Reed said.
From 18 months to 2-years, communication skills take big leaps - they're aware of people, know and can point to body parts, and string words together in simple sentences.
"They're also starting to interact with other kids," Larkin said.
More big changes take place between ages 3 and 4. Sentences are longer, kids learn the names of friends, teachers, and family members.
"The biggest thing parents can do to encourage development is to read," Larkin said. "That helps to get kids excited about learning."
Kids Health Matters: Milestones that parents should know
KIDS HEALTH MATTERS