Wow!
I can't believe that the OP can not understand why the airline would not allow an infant in the exit row...as if in the case of an emergency a parent would not put their child's interests first before helping other passengers out. What do they do, pass the infant to some other person in another row while they help the people out?!
And the other poster who couldn't understand why a 12 year old might not be an ideal choice as a person to help others...who knows how they might react in the case of an emergency? I would be more comfortable being helped by an adult rather than a 12 year old myself. And yes, yes, I know that not all adults are level headed in emergencies as well.
The last flight I was on, there was an elderly couple seated in the exit row. When the flight attendant came by and reminded them of their 'duties', she noticed that the woman had a cane. And had to be helped on the flight. She allowed herself to be moved.
Sorry, but I take those exit row responsibilities seriously when I sit there and think others who sit there should also.