What can cause uncontrollable shaking in children?

Seizure Disorder? You didn't mention the child's age, sex, type of shaking or jerking, duration, status of consciousness, color change, frothing in mouth, urinary incontinence etc. The child needs full medical evaluation; if epilepsy is a probability, eeg to be done and a pediatric neurology referral is needed. Contact your child's pediatrician.