Yes, I am sure that Carnival knows that once you have paid for the cruise, a $5 increase in the price of a character breakfast isn't going to change your decision to go, especially if you have little kids.
FTR character breakfasts at Disney are $60+ per adult. Granted, it is not exactly apples to apples, but again, once you have plunked down the $$$$ to book the hotel and get into the park, you're going to pay a few extra dollars for the meal to get the experience you want.