Physical abuse is also unfortunately common amongst multiples. Physical abuse includes some forms of spanking all the way through severe and repetitive physical trauma that can result in death. For chilling medical accounts of physical abuse that are quite obviously true, you can read up on Munchausen's Syndrome by Proxy. There is also no doubt that physical abuse takes place backed by religious edicts such as "Spare the rod, spoil the child." (Although how one can tell whether that's a commandment to stop abusing children and telling one to spoil them, or one that is a warning that if you don't abuse your children you'll be spoiling them is impossible to tell.)
Physical abuse often comes with other types of abuse. Rarely is the person physically abusing the child not also screaming or yelling, or throwing around heavy psychic attacks. Note that with Munchausen's Syndrome by Proxy, however, usually the parent is not displaying other types of abuse, although neglect is common enough (usually the person who has MSbP is histrionic personality disordered, which means essentially that they're pretty self-centered to the point of plausibly neglecting their children if they can suck up some of the limelight).