Can you breathe under water when you have just been born?

You can't.

Humans, of any age, can't breathe underwater w/o the aid of machines.

But babies have two things going for them. First it's something called the dive reflex that'll have them hold their breath.

Secondly, if they're actually born under water, they won't need to breathe as long as the umbilical cord and the placenta is intact. They've gotten their oxygen from the blood from the mother through the umbilical cord, since conception, and a few minutes longer will work just fine.