Sudden infant death syndrome (SIDS) is the unexplained death, usually during sleep, of a seemingly healthy baby less than a year old. SIDS is sometimes known as crib death because the infants often die in their cribs.
If a baby is forcefully shaken, his or her fragile brain moves back and forth inside the skull. This causes bruising, swelling and bleeding. Shaken baby syndrome usually occurs when a parent or caregiver severely shakes a baby or toddler due to frustration or anger — often because the child won't stop crying.