American Airlines is notorious for changing flights, flight times and seats. They have done this to us many times. My wife sometimes get airsick and she needs a window seat. One time they changed our seats which were together and placed me on one end of the plane and her on the other. If the new assignment isn't good for you then by all means change it. Let them know.
Some models of Boeing 747, 757, 767 and 777 have 'bassinet' rows. They are rows of seats with a bassinet in front of them for people traveling with babies - usually long distance flights, i.e. international.
the reason I spend the extra money for choice extra is that I am 6 feet 2 inches tall and it is my first time in a plane. I was thinking about switching both flights the one to Miami to get in at 11:50 am instead of 1:10 pm and take a latter flight that leaves at 3 pm on the back.