Use of Tu in first lesson

I sunderstood Tu is only used for close frends and children, yet in the first lesson it seems to be used instead of vous is this correct or is it simply used because Paul adn Claire know each other. In either case I think the use should be stated

Salut, thanks for your post. Yes, Paul and I are friends and therefore we address each other with "tu". Over half of the lessons of the Interactive Audio Course cover the formal form "vous". We do go into more detail on the different ways of addressing someone throughout the lessons, so I hope you will find it easier. Merci Claire