Refereeing for the first time tomorrow, and I'm so nervous help?

I just got a call from the convenor of my club and I'm refereeing for the first time tomorrow. The kids are seven. I'm so nervous! The course I took was an official FIFA course so I have no idea how to ref kids this young. Are there some calls that referees don't bother making when reffing kids this young? Will the parents hate me and yell at me? Someone please tell me what to expect