I hope Pixi isn't thinking you are doing anything to the baby. An infant's cry may imitate a cat cry to the cat. Or perhaps Pixi is alerting you to the fact the baby needs something, although attacking would not seem the proper way for a cat to get your attention. If you see an attack approaching, see if you can stop it with a firm and loud NO. Nobody likes to have scratches all over them, although I have them from giving Raiden medications twice a day (he hates it).
Gosh, if we could only understand what a cat is thinking.