Yawning while sleeping?

How come babys' yawn when they are already asleep?

Babies do all kinds of weird things. I was researching your question on ask.com and I couldn't really find anything. Yawning doesn't always mean you are tired though. My doctor told me excessive yawning means you are lacking oxygen and you need deeper breaths. How true that is, I don't know. We probably yawn in our sleep too, we just don't realize it. A sleeping baby dreams and just like us, we do things in our sleep like walk, talk, toss and turn. maybe they are simply dreaming of being tired. Who knows. I'll continue to search and if I find something I'll let you know

I dont know maybe they are still tired when they are asleep

No idea. I do it too for some reason.

My children use to yawn in their sleep and just thought it was because of the lack of oxygen.. Who really knows?

The real question is, why are yawns contagious?

When we yawn we are lacking oxygen just like these said.. and it is contagious becuase when you see someone yawn it sends a message to your brain telling you, you need more oxygen for some reason haha =S How weird... Anyway I feel clever now.. I learnt that yesterday at school HAHA =D