Why are yawns catching?

That's a very good question. Yawning is a really common reflex, actually that happens in lots of different animals. If you see someone yawning you want to yawn yourself which is very strange. We see it in all these animals including some that maybe aren't so social. Maybe it isn't something that's learned but maybe a bit more inherent. Perhaps it just starts to arrive at some point.Wild dogs in Africa get contagious yawning, where one will yawn and then the other will yawn and it tends to be about the time when they're going to bed. It's a nice way of getting the whole pack to decide to go to bed.

Often with very young babies, their eyesight isn't very good. They can't focus very well so it could be just she can't see you yawning. She doesn't learn how to yawn from that.