working with little kids

I have been working this summer at a local private school in their tutoring program. This program meets everyday for three hours in the AM. I work the first hour one on one and the last hour one on one. The middle hour is spent working with a small group of eight 5-7 year olds. Two are going into kindergarten and the rest are going into first grade. Well, the other day we were working on our lesson and one kid offers to pay me 2 dollars. Then the other kids offer to bring in money if we could not do what we were working on. At the time I was trying to not laugh cause it was funny seeing little kids trying to "pay me off" for good behavior. At the time one of my supervisor's was in the room and myself, the supervisor and my two assistants were all laughing. I told the students thanks for their offer but they should keep their money. Then they kept asking if I or any other grown ups had money with us, they think adults always have cash with them. It was pretty amusing.