first piece of advice is keep in mind how far a city block is and how good these girls are at walking. american girl is near the rock, i would suggest a trip to rock. center to see it and the ice skaters. magnolia bakery is in the area, you can get a cupcake there at one point. another thing in the area is st.patricks just across the street- depending on your religious views that may be out. radio city is in the area too and you can go online and look into a backstage tour if the girls are into theatre and dance. there are plenty of places to eat, it all depends on budget and what kind of cuisine your girls are willing to eat.
i was there yesterday and did something we have never done, we walked to the top of the stairs in times square and took pics. it was a load of fun and the view was great! the ferris wheel is fun but keep in mind you may have a long wait time, we did that once and had to wait over two hours after paying for our tickets to get on, not worth it. a lot of those stores at this point are just larger chain stores and disney is not open. i would instead suggest a walk up fifth to browse stores, maybe tiffanys and FAO- i think its more original than toys r us. you can also look at the windows at saks near the rock and then bloomies and bergdorfs i believe are up on 5th near fao- as is the plaza and the corner of central park. map out a route and have fun!