Dear friend,
This is a horrible old wives tale. It was started because cats will often sniff an infants mouth and the myth said they would "steal the babys breath". Also a baby's cry can sound like a kitten so the cat (ever curious) will go to investigate. If a baby is moving around, a cat, stimulated by the motion may accidentally scratch him. However, cats are MUCH safer to have around babies than dogs as dogs will often see babies and young children not a people but as prey.
I would not worry about a six year old cat and a new baby, beyond the accidental scratch.
Please let me know if you still have any questions. I will be happy to help.
Very sincerely,
Terri
Feline Healthcare Expert
Expert in feline health and behavior. 20 years experience with cats.