Why do babies suddenly cry or smile while asleep?

I think its never too early for them to dream... dreaming is just part of the human mind and they're born with it! I've heard they can even dream in the womb.

I think a baby's mind is more complex than we'll ever know. I'm on the side of them dreaming though. Just think, if a baby can recognize his/her mother's voice at birth, why can't he/she also be dreaming of it? A baby's dream is probably not as detailed as an adult's since they don't have as many experiences to draw from but I see no reason why they can't be dreaming from at least birth on. Perhaps when a baby smiles in his sleep it is because he is dreaming of his mother's voice and the image of her face. That alone would be enough to make a baby smile. If he cries out maybe he dreamed of a loud noise that scared him.

some people say dreaming others say gas. it's hard to tell but i beleive they can dream at this age, why not. dream about what they see or even heaven if you beleive in past lives or heaven they might be able to remember what it was like there cause they just came from there not too long before. it's a thought. i've heard a well knows spychic talk about this before