It was ALL a dream until Cobb woke up on the plane at the end. The movie’s first scene was the start of the dream, and it continued until he woke up in the plane at the end. The lines from the end were:
Caine: Have a nice flight then?
DiCaprio: Yeah, but I had this crazy dream. How are the kids?
Caine: Fine, just fine. Let’s go see them
the answer was never the top. Nolan did a great job making us focus on the top, but the truth was to focus on the background, in other words, the children. The kids are wearing different clothes in the end. Very slight and subtle differences but its quite noticeable once you focus on that. Throughout the movie, the girl wears a pink/peachy dress that has sleeves. In the end she is wearing a very similar dress but the difference is that the dress does not have sleeves and she is wearing a white undershirt. The boy’s shirt is different too