Not a medical emergency; can be treated by first aid responders
Usually occurs during or after exercise
Usually sart by affecting the specific muscles recently exercised
Can increase in severity by increasing the number of muscles affected
Probably results from
dehydration [1] (either from losses of fluid from sweat or lack of re-hydrating from a pervious exercise/play session)
electrolyte [2] loss through sweat
Muscle painor a feeling of "twinges"
Spasms
Visual evidence that muscles have tightened up
Remove child from practice or game and into the shade
Have the child sip or drink fluids with electrolytes [3] (sports drinks) continually until symptoms stop.
Avoid "sloshy" feeling or excessive drinking of fluids
Good rule of thumb: continue sipping after cramps stop until the child has the urge to urinate
Gently massage the affected muscles
Massage the affected muscles with ice bags (if possible, and if tolerated by the child)
Gently stretch the affected muscles
Add salt to foods (not by giving salt tablets)
Links:
[1] https://mail.momsteam.com/node/867
[2] https://mail.momsteam.com/865
[3] https://mail.momsteam.com/alpha/features/nutrition/electrolytes.shtml
[4] https://mail.momsteam.com/health-safety/hydration-safety/cancel-modify-games-practices-heat-humidity
[5] https://mail.momsteam.com/nutrition/heat-illness-cramps-exhaustion-stroke-signs-treatment