Well, what does she expect with 34 kids in the same classroom? That's insane!!!
With 34 kids, the teacher needs to learn how to control her class, and she needs to do it yesterday. If she can't handle a couple of kids talking too much, this is going to be a very painful year for everyone!
Ok, first, do talk to your kids about the importance of respecting the teacher, following rules, paying attention, not being disruptive, etc. When the teacher asks them to be quiet, it's really important so that everyone can have a good day. We respect the rules of each place that we go to, and the classroom is a very important place to follow the rules.
So that's what you say to your kids. What you say to yourself is, "This is not my problem. The teacher needs to handle this, and I will support the teacher." The teacher needs to handle this, but you need to make sure the kids never see you waver of your support of the teacher and her decisions. It doesn't matter whether you agree with all of her decisions or not, the kids need to think you do!
Too much talking in class is very common. They will mature. If you keep reminding them, they will get better. It is ridiculous that the principal called you. Talking in class is very normal. The teacher and principal need to learn how to deal with this.
Did the principal mention suspending them? There are some first graders causing real problems in this world - physical violence, bringing a gun to school, etc. I'm just shocked that a couple of chatter boxes are really this much on her radar.