Stay warm little baby birds

I went out at 7am (in my jacket) but I thought it was too chilly to stay out long. I could hear the baby birds cheeping today when their food was brought. (Yesterday I couldn't hear anything, they were still too new- but now they are 1 day old they are cheepers)
I hope they keep warm as I was chilly in a jacket and they are naked baby birds, but at least they are in a nest.
I'm going back outside when my baby wakes up, because he'll need to be fed. And his cheep is louder than the baby birds.