Dehydration affects two of out three children, according to the National SAFE KIDS Campaign, through its "Defeat the Heat" public safety campaign.

"You have the whole gamut from heat cramps or heat stroke or death," said Billie Tang, who is a physical therapist and athletic trainer. "And it is so preventable, you just have to know about fluids."

Tang, with the Keiki Injury Prevention Coalition, was one of several volunteers at the "Defeat the Heat" tent at Waipi'o Peninsula Soccer Complex at the American Youth Soccer Association Rainbow Tournament earlier this month.

She said most parents and coaches are unaware how much fluids — both water and sports drinks — children need, especially in a hot and humid climate like Hawai'i.

"They set the example," Tang said. "If a coach isn't allowing you to drink water, what are you going to do?"

One of the best indicators of lost fluids during activity is weight loss. Tang said the 450 children who visited the "Defeat the Heat" tent were weighed before and after their games. Losing more than a pound was an indication of improper hydration.

Losing a little weight is natural, according to Dr. Spencer Chang, an orthopedic surgeon who specializes in sports medicine.

Chang, who helped out at the tent, said "replenishing is the key."

He said sports drinks help replace lost electrolytes. However, he cautioned to stay away from caffeinated soft drinks because they are diuretics and won't hydrate you.

He also said to drink cold water to try to cool your body down.

Chang, who also helps out as a team doctor at the University of Hawai'i, did his fellowship with the University of Miami football team, and said he saw first-hand some of the dangers of dehydration.

Florida is similar to Hawai'i because of its humidity, and he said some of the players became so dehydrated they needed to receive 2 to 3 liters of fluids intravenously.

If dehydration is not addressed, it can escalate to heat cramps, heat exhaustion, or exertional heat stroke, which can result in death.

Courtney Frederiksen downs a sports drink during a break in her soccer game at Waipi'o Peninsula Soccer Complex.

Heat cramps can include symptoms such as intense pain and persistent muscle contractions. Cramps can be treated with light stretching and massage.

Heat exhaustion is moderate heat illness that occurs when a child continues to be physically active even after he or she suffers from the effects of the heat, like dehydration, according to the National SAFE KIDS Campaign.

The worst-case scenario is exertional heat stroke, which occurs when a child's body creates more heat than it can release. It can lead to permanent disability or death if left untreated, according to the National SAFE KIDS Campaign.

If a child's temperature rises above 104 degrees or he or she has seizures, confusion or irrational behavior, you should seek medical treatment immediately.

Kailua Intermediate student Trey Tam, 12, said he will drink more fluids after learning what could happen if he doesn't drink enough.

His father, Ranson, of Waimanalo, was happy for the education.

"He sweats a lot, so we always tell him to drink plenty," Ranson Tam said. "This educational stuff will help out. If you see the pro football players, they have a lot of accidents. I don't think a lot of parents know about it."

According to the campaign, children with different body weight need different amounts of water.

Children under 90 pounds should drink 3 to 6 ounces one hour before an activity, 3 to 5 ounces every 20 minutes during an activity and up to eight ounces after the activity, per half pound of weight lost.

One ounce usually equals two child-size gulps.

Children over 90 pounds should drink 6 to 12 ounces one hour before an activity, 6 to 9 ounces every 20 minutes during an activity and up to 12 ounces after the activity, per half pound of weight lost.

It is something Kailua freshman Melanie Yoshida will have to take into consideration.

Yoshida, 14, said she gets dehydrated a lot, although she tries to drink Gatorade before and during games.

"I already kind of knew about it, but I didn't know how much I needed," she said. "I need to try to drink more water."

Symptoms of dehydration include the obvious, such as thirst, and a headache and dizziness, according to the National Safe Kids Campaign.

Some signs that aren't as obvious are: becoming seemingly bored or uninterested in the activity; or the child being unable to run as fast or play as usual.

King Intermediate eighth-grader Kekoa Bonds said he didn't know the symptoms of dehydration before, although he drinks a lot of water because his mother encourages him to.

"I was just drinking it before," said Bonds, 12. "But now I know why."