Answer:
I keep things green and keep kids happy during summer time.
I'm blue, but when you see me I'm red. You don't see me too often. I'm there for you if you're hurt, but I'm good for you. What am I?
I am free the first time and the second time, but the third time is going to cost you money. What am I?
Take off my skin I won't cry but you will. What am I?
I belong to you but others use me more often than you do
No matter how little or how much you use me, you change me every month.