according to http://www.askdrwarren.com/qa040503.htm#q6
Night Leg CrampsDr.: My daughter is three year old and every other night or so she awakes with leg and/or foot cramps. Is this normal? What medication should I give her? if any
Thank You for your time.
Dear RC: Nighttime foot and leg cramps are fairly common in children. They occur as a result of spasm in muscles that have been used a lot during the day. The best thing to do is massage the cramp. If your daughter has daytime pains, pains that interfere with activity, or a limp then she needs further evaluation.
Make sure the covers are not tight over the foot of the bed as that makes it necessary for the child to stretch his foot out and may contribute to the development of cramps.