By the sound of it, everything about what the kids said in the final scene was designed to either feel thematically relevant to the movie’s big questions or to reinforce the idea that these are very much Cobb’s kids. The movie doesn’t actually spend much time with them, after all, so when it comes to making us believe that they’re a driving force behind so much of Cobb’s motivations, the movie really had to do as much as it could with the little time it had with them. Even the objects on the table revealed so much about the kids’ personalities (like the fact that they like to play with the blocks), to help reinforce a sense of connection between them and Cobb. Just as Cobb’s made a career out of building things in the dream world, his kids have that building instinct in them too.
“Everything is about how they would create, whether it’s blocks or sand castles or a dream. These are all acts of creation,” Nolan explained. “There’s a relationship between the sand castle the kids are building on the beach in the beginning of the film and the buildings literally being eaten away by the subconscious and falling into the sea.” Dreams tend to ebb and flow through a person’s memories, taking them from one setting to another in ways that might seem jarring at first to an outside observer, and that’s exactly the feeling “Inception” tries to invoke constantly throughout Cobb’s journey. As Nolan continued:
“The important thing in ‘Inception’ is the mental process. What the dream-share technology enables them to do is remove physicality from that process. It’s about pure creation. That’s why it’s a film about architects rather than soldiers.”