Athletes who exercise in hot or humid weather are prone to three, progressively more serious, heat illnesses:

• Heat cramps
• Exertional heat exhaustion
• Exertional heat stroke

Symptoms of impending heat illness

In addition to educating young athletes about both the importance of hydration and the dangers of heat-related illness, ensuring that they drink enough fluids [1], and taking precautions [2] to reduce the risk of heat injury in children in hot and humid weather, you need to watch your child for symptoms of impending heat illness:

• Fatigue and tiredness
• Chills
• Nausea
• Headache
• Disorientation
• Muscle cramping
• Lightheadedness
• Dizziness
• Thirst
• Grumpiness and irritability
• Feeling hot
• Trouble concentrating

A child continuing to exercise when experiencing any of these symptoms could suffer a heat illness. 

Heat Cramps

Overview

• Painful muscle spasms
• Not a medical emergency
• Can be treated by first aid responders
• Usually occurs during or after exercise
• Usually starts by affecting specific muscles exercised
• Can increase in severity by increasing the number of muscles affected
• In severe cases can involve all skeletal muscles in the body
• Probably results from
  • Dehydration (either from fluid losses from sweating or failure to re-hydrate during or after sports)
  • Electrolytes lost through sweat (salt, potassium, magnesium etc.)
  • Fatigue
• No medical attention required
• Usually occurs during or after exercise
• Usually affects only specific muscles exercised
• Probably results from an imbalance of the body's fluid and electrolyte [3] concentrations caused by a loss of electrolytes in sweat.

Symptoms:

• Muscle pain or feeling of  "twinges"
• Spasms
• Visually seeing muscles tighten
• Possible nausea and thirst as result of dehydration occuring at same time

Treatment:

• Remove from practice, game or exercise
• Move child to shade
• Have child sip or drink fluids with electrolytes [3] (sports drinks) [4] continually until symptoms stop
  • Child should avoid excessive fluid consumption (feeling "sloshy")
  • General rule of thumb: continue sipping or drinking after cramps stop until the child has the urge to urinate
• Gently massage and stretch the affected muscles
• Apply ice bags to affected muscles, if tolerated
• Add salt to foods (not by giving salt tablets [5])
• If symptoms continue and/or child cannot tolerate fluids by mouth, take child to hospital or doctor (no need to call ambulance)

Exertional Heat Exhaustion

What is heat exhaustion?

• A serious heat illness
• May require medical attention
• Probably results from a reduced blood volume due to excessive sweating, which causes blood to pool in the extremities, causing the child to faint or feel dizzy.

Heat exhaustion symptoms

• Nausea
• Extreme fatigue or "jelly legs"
• Headache
• Shortness of breath
• Weak, rapid pulse
• Thirst or dry mouth
• Rectal temperature less than 104 degrees F.

Heat exhaustion treatment:

• Remove child from practice or game
• Move child out of sun to a shady place
• Have the child sip or drink fluids containing electrolytes [6] (sports drinks) until the symptoms are gone
  • Avoid excessive drinking (child has "sloshy" feeling)
  • Good rule of thumb: have child continue sipping after cramps are gone and child has an urge to urinate
• Remove excessive clothing
• Cool (mainly for comfort) the child with fans, cold towels/sheets, misters, or ice bags on arms or legs
• Hold the child out of playing or exercising in the heat for at least one full day.  Hold out longer if they experience any symptoms when they try to return.
• Seek medical attention, if no improvement within 15 to 20 minutes

Exertional Heat Stroke (Exercise-Induced Hyperthermia)

Overview

• Life-threatening medical emergency
• Body's temperature is too high
• Left untreated, exertional heat stroke results in death due to organ damage across all body systems (liver, kidney, brain, etc.)
• Until medical help arrives, the key is to immediately lower elevated body temperature

Symptoms

• Excessively high rectal temperature (over 104 degrees)(oral, axillary, tympanic, and temporal measurements are innacurate and cannot be trusted)

And any or all of the following:

• Erratic pulse (strong and rapid or weak and rapid)
• Lack of coordination
• Collapse
• Low blood pressure
• Vomiting
• Headache
• Loss of consciousness and/or seizure 
• Shock
• Irritability, confusion, disorientation
• Sweaty skin that may be red/flushed or pale

Treatment

• Call 911 [7]
• Remove all excessive clothes
• Ice-water or cold-water immersion [8] with water continually circulating  in:
  • Large stock tank or Rubbermaid container [9]
  • Baby pool
  • Bath tub
  • Pond
  • Creek
• When not feasible, immediate and continual dousing with water (either from a hose, multiple water containers or shower) combined with fanning and continually rotating cold, wet towels on head and neck until immersive cooling can occur.