INFANTS

Infants need to visit a pediatrician more often than the typical annual check recommended for children. Doctors say they should be seen at two weeks and then at one, two, three, four, six, nine, 12, 15, and 18 months of age. During the first two years, doctors measure the baby’s height, weight and head circumference. Typically, they will also listen to the heart and lungs and check the size and location of organs.

Infants also get many immunizations. Newborns should receive the hepatitis B vaccine son after birth and before they leave the hospital; they should get their second dose at one to two months and their final dose around 24 weeks. At two, four and six months and then again by 18 months, they should get their diphtheria, tetanus and pertussis (DtaP) vaccine. At two months, they start getting their first of four inactivated poliovirus immunizations. At two, four and six months, they should get the rotavirus vaccine to protect them against an infection that can cause severe diarrhea, vomiting, low-grade fever and dehydration. At 12 months, they get their first measles, mumps and rubella vaccine. And at 12 to 15 months, they get their first varicella (chicken pox) vaccine. At two months, babies get their first in a series of pneumoccocal vaccines. And between 12 and 23 months, kids should get two doses of the hepatitis A vaccine (HepA), given at least six months apart. (More information is available at the Web site for the American Academy of Pediatrics.)

Doctors also recommend that parents start recording developmental milestones and concerns to discuss them with the pediatrician. "We only get a snapshot of your child [during a visit]," says Texas pediatrician Ari Brown, co- author of "Toddler 411" (Windsor Peak Press, Aug. 2006).

TODDLERS

Toddlers still need checkups when they turn 2, 3 and 4. After age 2, doctors measure height, weight and blood pressure rather than head circumference. They also conduct a lung, chest and genitalia exam and look at reflexes. And they look for signs of developmental disorders and autism. For more information on warning signs of possible developmental delays, see the Centers For Disease Control (CDC) Web site.

Doctors may also talk to parents about developmental milestones for toddlers. Kids who are 2 and 3 years old, for example, should be able to sort objects by shape and color and obey short commands. Kids who are 3 to 5 years old should be able to ride a tricycle, use safety scissors, help dress and undress themselves and play with other kids. Doctors may also talk to parents about positive parenting at this age, such as reading to kids and letting them help with simple chores.

Expect to see doctors refer to the 2000 CDC Growth Charts to assess kids' nutritional status and general health as they get older. To see more information about the charts and to figure out your child's body-mass index, go to cdc.gov/growthcharts/.

ELEMENTARY-SCHOOL AGE

Typically at the 5-year checkup, kids get any remaining immunizations that their state requires for school entry. (Click here for a chart of your state's requirements.) In June, the Advisory Committee on Immunization Practices (ACIP) to the CDC voted to also recommend a second dose of chickenpox vaccine to kids who are 4 to 6.) Elementary- school kids often go for checkups every year, though pediatricians say it's acceptable if healthy kids only go at 6, 8 and 10. Doctors will ask kids for urine specimens to look for protein and blood—symptoms of kidney disease. (Contrary to popular belief, they are not using the urine specimen to screen for diabetes.)

TWEENS

Most kids enter puberty healthy; the annual physical helps keep it that way. The 2006 Childhood and Adolescent Immunization Schedule—released earlier this year by the CDC, the American Academy of Pediatrics and the American Academy of Family Physicians—includes several additions for 11 and 12-year-olds. They should get the meningococcal conjugate vaccine to reduce the incidence of a rare but potentially lethal bacterial infection, as well as the new tetanus, diphtheria and acellular pertussis "booster" to protect against whooping cough. Adolescents who haven't received all three doses of hepatitis B vaccine should start or complete the series. (Leave at least four months between the first and third doses.) Check whether your insurance carrier is already covering the human papilloma virus (HPV) vaccine, which the Centers for Disease Control recommended in June and which costs $360 for a series of three shots given over six months. A CDC advisory panel has recommended it for girls aged 11 to 12 and for 13- to 26-year-old women who have not yet received or completed the vaccine series.

At their checkups, tweens may want to talk to their doctors about why they have pimples or when they will get "grown-up bodies," says Robie Harris, author of "It's Perfectly Normal" (Candlewick; 2004). Doctors can explain what hormones are and may also talk to tweens about delaying sex and about getting pregnant or contracting a sexually transmitted disease. Many doctors like time alone with children, starting at age 11 or 12, to ask confidential questions. Some also want time alone with parents, who may not want to talk about their concerns about drug use or sex in front of their children. "Everyone has to agree that we have some ground rules for confidentiality," says Dr. John Knight, director of the Center for Adolescent Substance Abuse Research at Children's Hospital Boston. "I'm going to keep their responses private unless there's a safety issue."

Many doctors also use written questionnaires to gather information in a nonjudgmental way.

TEENS

Teens should catch up on any missing immunizations. Some states require the meningococcal conjugate vaccine (MCV4) for college students. Currently, demand for Sanofi- Pasteur's vaccine exceeds supply. So the CDC is recommending that high school students and college freshmen living in dorms get the vaccine.

During the teenage years, doctors also like to make sure their patients are maintaining healthy habits and avoiding risky behavior. (Some doctors specialize in adolescent medicine.) Dr. Cynthia Mears, a board-certified adolescent medicine specialist at Children's Memorial Hospital in Chicago and at Northwestern University, says she asks teens about smoking, sex and drinking. "You're trying to get kids to think about what they do and to be responsible for their health," she says. That's good practice for adulthood, when their health will be in their own hands.