Personally, I congratulate AMC for charging for babies.

Bringing a young child to a movie-- particularly one with as much violence as the Narnia films-- is like playing Russian Roulette, only you're only pointing the gun at everyone else in the theater.

It's very nice that YOUR child didn't start crying or fussing and only slept through the movie quietly, but other people's children are not so easy to please.

Part of the benefit of that charge is that it deters people who ignore the impact their children have on the rest of the world.

If your child is too young to appreciate movies, why even bring them in the first place? Find a babysitter, and spare some quality time with your nine-year-old, who is probably getting less attention
than his new baby sister anyway.