My Mother Cat attacked a crying baby..And now my other cat. Why?

new mothers are always very defensive of their kittens. my own cat, who is usually very gentle used to bite anyone who came near her kittens, even other cats who aren't a threat and she's used to, she'll bite and scratch at them and chase them away. maybe she mistook the baby's crying or the sound of an animal about to attack, and immediately got into defensive mode. don't worry, it's completely normal for cats. even humans will get defensive when it comes to their babies, only cats are even more sensitive and sometimes they can't differentiate between what's an actual threat and what isn't