FALLS CHURCH, Va. - Physical activity helps children build strong bones and muscles while maintaining a healthy weight. But every year, sports and recreational endeavors lead to as many as 1 million to 2 million concussions in children younger than 18, according to a recent report from the American Academy of Pediatrics.

A concussion is a mild traumatic brain injury caused by a blow, bump, or jolt to the head. Most children under 18 will recover fully from a concussion with no lasting health effects, according to the Centers for Disease Control and Prevention. However, it may take children longer than adults to recover from a concussion, the CDC says.

Here are some facts about children and concussions:

Loss of consciousness may be so brief that it’s not noticeable – "like feeling stunned," said Dr. Bradley Dengler, an Army major and director of neurotrauma and neurocritical care at Walter Reed National Military Medical Center in Bethesda, Maryland. Other symptoms of concussion, according to the CDC, include feeling dizzy or confused; experiencing problems with balance, vision, or motor skills; and sleeping more or less than usual.

Signs of concussion can occur immediately after a head injury, Dengler said, or days and even weeks afterward.

This imaging test determines if there’s also internal bleeding or a skull fracture, said Dr. Tony Kim, an Air Force colonel and assistant professor in the Department of Military and Emergency Medicine at Uniformed Services University of the Health Sciences in Bethesda, Maryland. Kim said it’s more common for physicians to scan elderly people who have head injuries because the brain shrinks as people age. As a result, there’s more room in the skull for the organ to jostle around and cause vein tears that lead to bleeding.

With young children, Kim said studies have shown the majority of concussion cases don’t result in skull fractures or internal bleeding. "So the decision for scanning is based on using prediction scores," such as the PECARN Pediatric Head Injury Score.

"If the prediction score is low, that means the likelihood of finding an injury needing neurosurgical intervention is also low," Kim said. "So it may be more harmful to expose the child to radiation from the scan."

"The best treatment for a concussion is brain rest," Dengler said. "That means staying out of school and certainly staying out of sports, or not exerting yourself, until you’re back to normal. Kids should be able to exert themselves without getting a headache."

"I know it’s boring and difficult for kids in this modern era to sit and do nothing," Kim said. "But the brain just needs to rest. So no loud music, no stimulating lights, no video games, no smart phone use or social media."

Without adequate healing time, the risk increases for post-concussion syndrome. "It can last for months," Kim said. Symptoms include persistent headaches and intermittent nausea.

The CDC has developed a mobile game app to teach children ages 6 to 8 about concussion and brain safety and has a concussion information sheet for parents.

Also, children who resume vigorous activities too soon after getting a concussion are at increased risk of getting another one, according to the CDC. Multiple concussions can lead to long-term brain damage including loss of memory and problems with organizational skills, such as keeping track of homework papers, the CDC said.

"The more concussions you get, the worse the long-term damage is going to be," Dengler said.