I think it would be fine to charge for the scavenger hunt. It sounds simple enough. Everything we have at our carnival brings in money. Tickets are 50 cents and covers games, cake walk, fortune teller, tattoos (because face painting became alot of work) and balloons. We also sell food but they require more tickets.
We have a silent Auction, but it's really needs to be revamped, I think we made $200 on it last year and had alot of items that weren't bid on at all and we had no reserve
But our raffle was by far the biggest money maker. Students sold tickets for $1 and the winner had the choice of an Xbox 360 or a 32 inch TV. They picked the Xbox of course. We sold $1200. in raffle tickets. This year we decided to raffle off a laptop.
We have other events during the school year that we don't charge for, Trunk or Treat and movie night among other things. But parents expect to have to pay at the carnival. I think we'll try the coloring table this year, thanks for the idea!