What are the chances of my child having a development problem?

Not very high. Less than 3.4 percent of all children under age 5 have a developmental delay and these children have a substantial delay in their physical, mental, or cognitive development. This includes problems with chewing, eating, using the toilet, understanding language, expression, following instructions, participating in strenuous activities, or moving around. Children under age 5 who only have a hearing, vision, or speech impairment are not considered delayed.

If my child does have a delay, what could be causing it?

That depends on whether the problem is physical or cognitive. A physical delay can be a symptom of a larger disability, such as spina bifida or autism — but it can also simply mean that your child needs a few more weeks or months to catch up to his peers. Some children will have delays in a particular area, such as walking, while the rest of their skills continue developing on or ahead of schedule. If that's the case for your child, it may just mean he's concentrating so hard on talking or understanding that walking is just not so important for him yet.

Language and other cognitive delays can be difficult to pinpoint at a young age, but it's important to catch them early so they don't lead to other, long-term problems. Some children have difficulty with receptive language — understanding the meanings of words and sentences, and others struggle with expressive language (expressing ideas in words and sentences). Problems might stem from a hearing impairment, a problem with the central nervous system or brain, or a problem with the larynx, throat, nasal, or mouth. The average language development timetable is broad, though, and it's perfectly normal for your child to run into small difficulties along the way. As long as your child can speak clearly by the time he's 7, he's on track.

If your child was born prematurely, keep in mind that he might sometimes need a bit more time to reach the same developmental stages as other kids his age.

What early warning signs should I watch for?

Familiarize yourself with the normal timeline for developing cognitive and physical skills, and follow your instincts. You know your child best, so you're likely to spot problems early. Is something in particular bothering you about the way your child is walking or talking? Does it seem that he has lost a milestone that he already attained? Have you noticed any specific signs of a physical delay or signs of a language or communication delay?

What should I do if I'm still worried?

If you think something's wrong, don't assume your child will outgrow it. Call your child's pediatrician to discuss your concerns, and schedule a checkup. Carefully explain what you've observed and see what the doctor says. She may be able to calm your fears quickly, or she may ask you to come in for an evaluation or developmental assessment. She might also refer you to a pediatrician who specializes in development issues. Even if she doesn't, you may want to consult one — a second opinion is never a bad idea. If you think your child has a language or communication delay, you can also go directly to a speech pathologist for more information and advice.

Keep in mind that vision and hearing problems are hard to spot unless you're a professional, so eye and ear checkups should be part of every doctor visit.