What is the philosophy of the movie Up?
Ellie is clearly a lot more adventurous than Carl. In fact that is clear in the first few minutes. To Carl, "Spirit of Adventure" is a balloon and for her its an abandoned house. The size, I think, matters because that is the size of the spirit of adventure.

Another thing alluding to her spirit of adventure is the loss of the baby and her subsequent rebounding from the sadness. She takes this grave loss as an adventure in her book. Carl is a good husband to point out that she needs to fulfill her "Things I am going to do" promise to herself, but does not realize how Ellie views the loss of the baby.

Carl is stuck on the aspect of having the house on Paradise island. He thinks that Ellie never lived her adventures and never added to her book since her first wish never got fulfilled. 

When an adventure presents itself in the form of Kevin, Carl, still attached to the past, prefers to fulfill the perceived wish by Ellie. When he does get the home on the water fall, it is clear that he is not satisfied. He can say that the dog nor Kevin are his problems. But when he sits down in his beloved chair, and looks through Ellie book of adventure again, he realizes that Ellie lived her adventures. She had no regrets. Her life was an adventure. And just at the right time, Carl sees the message from her to live his own adventure, i.e. Kevin.

Things become clearer for Carl. He is absolved of his guilt. He realizes that Ellie never felt bad about not being able to have her home on Paradise island. This moment of clarity is what all humans crave for. With this clarity, it was easy for him to be rid of all his attachments. He left behind his and his wife's chairs that he is clearly very attached to.

The message here, at least for the adults to discern and then communicate to the kids is to live your life. Yes you have dreams. But in day to day life, those dreams may not be achieved. Look for adventure. Look to live fully and without attachment to your dreams like Ellie did. Because, then, in living this full life, it just might be that your dream comes true. It just might be that the house is on Paradise island even without you trying like in the end of the movie!