Some theater chains do require tickets for children and babies because of the annoyance that a crying baby or talking toddler can cause to others trying to listen to the movie. And one chain I know of does not allow children under 5 into PG 13 or R rated films. A 2 year old will start talking to his parents (or just to hear him/herself talk) because he/she does not understand the film and is bored. And some people are simply too cheap to hire babysitters, so they bring their crying, bawling, or chattering babies/toddlers to the movie theater with them. If I'm trying to listen to a film, a crying baby or chattering toddler can be an annoyance. It's just as bad as someone using a cell phone during a film. I don't blame AMC for charging babies/toddlers for admission. And a film like "Chronicles Of Narnia" would be too complex for a 2 year old to understand. Sure the child may be sleeping through the film, but he/she might wake up and start talking. And AMC does include this message during the previews: "Please don't spoil the movie by adding your own soundtrack."
Sorry for the rant, but talking or crying babies during a movie is one of my biggest pet peeves.