be calm, have faith your child will be able to adapt. don't show your anxious mood to the kids.. assure them you will see them after school and chat with them about how's their day in school and see what kind of help they require.. communication is super important..
Inculcate values, beliefs and morals you want them to have and grow up with. Teach them right from wrong and how to stand for their own belief system so that peer influence for the worse will find it tough to take root.