You will be learning together so enjoy that experience. The kids at that age just love playing so try not to be picky unless it can be beneficial to game control. Also I have found advantage is practically useless as they don't understand it so much so try to measure when the game needs to be stopped if it really needs to be. The same goes for offside etc if it is used. The coaches will usually be a lot more into working with you at this age to make the kids' playing experience as smooth as possible. If a player does go too far in your opinion, discuss it with the coach at the time if you can and even ask them to make a sub of the problem player until they're less volatile.
Talk them through the game as much as you can, I know it isn't your job, but it creates a good relationship with the players and the coaches - however don't try to coach the players and try to explain your decisions to them, but as quick as you can! Never ever shout, and smile as much as possible! Try to keep your temper even if the parents etc are on your back. Remember they are children and should be protected as much as possible under your care on the pitch. At that age though it is everyone's responsibility to make sure they are safe. But really as I say again... all they want to do is play football and the rules come second!