A. You can respond by, getting heavy, playing along with it, or ignoring it.
Don't let them realise it's getting to you. Be firm and never forget that you're the teacher - even if there isn't much difference in your age, there is a huge professional distance. It's tempting to handle the boys with a withering put down, but it might encourage more banter. Ignoring it might be easiest. Seek advice from someone in the school, such as your induction tutor, who knows you and the boys.