Because half of all children with autism (search) or similar developmental disorders aren't diagnosed until age 4 to 6, the Centers for Disease Control and Prevention on Monday was launching a campaign to make doctors and parents aware of the need of early diagnosis.

Children can be diagnosed as early as 18 months old.

The CDC is working to fill doctors' offices around the country with posters and checklists that describe developmental milestones for each age. The agency also created for parents a height chart with similar information.

The health agency places autism in a category called autism spectrum disorders (search). People with such disorders may have problems with social, emotional and communication skills. The disorders can begin in early childhood and last throughout life.

For example, the CDC's information for parents says a 2-year-old should be able to point to an object when named, use two- to four-word phrases and follow simple instructions. A 3-year-old can imitate adults and playmates, play make-believe with dolls and use pronouns or plural words.

"It's important for families and providers — if a child has a developmental concern, early intervention really can have a positive impact," said Catherine Rice, a behavioral scientist with the federal health agency. "It doesn't necessarily cure or clean up the issue, but it can help the child to a higher level" of learning and living.

About 24,000 of the 4 million children born each year eventually will be diagnosed with autism or other developmental disorders. The agency estimated that up to half a million Americans under age 21 have an autism spectrum disorder, the CDC said.

The agency says it's a pressing issue because more children than ever before fall into the category of autism or autism-related disorders, primarily because medical officials and the government widened the definition of autism in the early 1990s.

CDC officials want to make sure parents and doctors know what to look for. If parents or doctors think there could be a developmental problem in a child, they should contact a developmental pediatrician, a specialist or a local early intervention agency, the CDC said.

"It's become more clear in the case of autism that it really is an urgent public health concern — before we used to think of it as a pretty low public health disorder; it's much more common than we previously thought," Rice said.

The early detection campaign will help educate doctors about when to diagnose the condition. Doctors know a lot about autism but many times it's not recognized until later, said Joe Guzzardo, spokesman for the National Alliance for Autism Research.

Tiffany Fleming knew something was wrong with her son, Connor, when he was just 6 months old. He would let loose bloodcurdling screams with enough emotion and intensity that he would turn purple and shake.

Connor's screaming continued. The Duluth, Ga., boy earned the title of one of the "Top 10" screamers at his doctor's office. Other strange behavior developed — he would repeatedly open and close drawers and it seemed like he didn't know how to play.

At age 2, Connor was diagnosed with a form of autism. After therapy and a special diet, "he started learning how to be a kid," Fleming said.

"It was like his brain was able to be rewired," said Fleming about her son, now 6. "If he hadn't been diagnosed and we hadn't started with early intervention, I can't imagine what he'd be like today — so much happens early."

In Duluth, Connor now attends preschool and Fleming said her family and doctors are happy they "were able to stop a lot of stuff before it manifested."

"He's very social, very cute, and has lots of friends," she added. "His biggest trouble is he wants things his way ... he has some extra anxieties but just overall, he's just an amazing, sweet kid. He's still a work in progress, but aren't we all?"