Don't push the panic button if your child looks a little heavy while she is still growing. Children can go through growth spurts that can add weight that is not necessarily unhealthy. The American Academy of Pediatrics recommends that children age 2 and older have body weight assessed at least once a year. To do that, health professionals often use a weight-to-height measurement called the body mass index (BMI). To calculate BMI and find out if your child is in an overweight or obese percentile for kids between the ages of 2 and 19, go to the CDC's calculator.