First thoughts right after watching the Movie
My first thoughts about this interaction right after watching the movie Up is that it is very unique with creating a fatherly/son dynamic between two people who do not share that kinship, and make it extremely organic. So many other films fail to pass off what Up did in regards to this, and it is the heart of the film. Pixar made another memorable relationship for the history books.
Summary
We first see them interact when the child knocks on the door, reading his boy scouts book, before offering help (which is so he can get his elderly assistance badge). Despite Carl slamming the door in his face twice, Russell literally repeats his dialogue, and Carl tricks him into leaving by getting him to catch a bird. He also turned down his hearing aid during this point in time.
Russell conveniently ends up outside on the porch once Carl sets his house to the sky (despite not being there before they landed), and offers to go in the house. The old man slams the door, only to open it a few seconds later to let him in. The kid steers the house around in excitement, which of course irritates Carl. After claiming that he could touch a building, Carl uses this as an idea to get him off, but it fails.

Of course this is going to take a while, and Carl realizes that he’s stuck with the kid, since there is no bus that will take him from the Amazon to the United States. Carl of course does not take Russell seriously when he mentions a bird that likes chocolate, but he is stuck with the bird, who takes a liking to the child. He tries to ditch the bird named Kevin and dog named Doug, which Russell whines about, but of course they manage to catch up. I never realized that Russell is literally how Carl was when he was a child; adventurous, a bit awkward, and shy.
After a failed attempt to make a pitch-tent, Russell reveals that he has never made a tent or went to camp before, because his father never wants to spend any time with him. Carl instantly feels bad for him after realizing that his father is never around, and the child does not have a mother; only a stepmother named Phyllis. Russel says that his father promised him to attend his badge ceremony once he assists the “elderly assistance badge”. This scene gives Russell another side to him that I honestly did not expect, and the dynamic between the two instantly change after this.

So in order to fetch after Russell, Carl has to “not-so-subtly” purge the old in his life for his house to float (to move on with his life). The kid ends up getting captured, Carl breaks into the ship, a final battle ensues, which we all know what ends up happening. I somewhat hate third acts in general (if you guys have not noticed yet) because of how predictable it is, and the first two acts are generally more interesting in general.
In the epilogue, Carl attends the ceremony of becoming a senior badge instead of his father (putting the pin on him), and from the disheveled looks of their appearance, they just made it back to America, and has no other time to prepare. The film ends with the two eating at the ice cream shop Russell did with his father in the past (even eating the same type of ice cream). We see the end credits are filled with moments of the two strolling through the city, fishing, going to a camping museum, relaxing at a park, staying at the retirement home Carl lives at, Carl reaching a bunch of boy scouts, watching Star Wars in theaters (very clever Disney), Russell teaching him how to use a computer, vising the zoo Carl and Ellie used to work at.
Final Thoughts
I have said beforehand that Up is not one of my favourite Pixar films, and I do not hold it to a high regard in comparison to most others, but Carl and Russell’s interactions hold and carry the film in regards to heart, message, and depth. And despite the father and son dynamic, they use many avenues to connect the two together in regards to common interests, loneliness, so on and so forth. Overall, they are one of my favourite interactions from Pixar, and they just continue to prove that they pull unique off better than almost anybody else.
They do have a unique relationship; I’ve always liked relationships that involve grumpy old men with younger friends, lol.