My kid age 2 yrs sometime get scared in sleep.cried.body stiff.jerks too.but he is in sleep.whats the best way to relax him?

Take your son & a : Video of the stiffening/jerking movements to his pediatrician, who will tell you if he needs an overnight eeg to rule out nocturnal seizures. If it's a night terror, you can put your child in his own bed, drowsy but awake, at a consistent time after reading, soothing & brushing his teeth. If he's having night terrors, he'll have no recollection of them & you'll get a full night's sleep.