Children sleep with a startle, the following common situations: 1, belongs to the normal phenomenon, because the baby is young, the cerebral cortex development is not yet perfect, easily affected by the surrounding environment or light and other stimuli, so that the phenomenon of limb trembling, with age, the cerebral cortex development is perfect, the ability to control the limbs will gradually improve, gradually disappear. 2, vitamin D deficiency rickets, will be manifested as a startle jump The baby is prone to excessive limb activity and easily frightened, accompanied by intellectual backwardness and other phenomena, and should be seen in hospital in time.