In Up, some of the serious topics dealt with include miscarriage and depression that follows. Ellie found out that she was pregnant and she was so happy that she decorated the entire nursery at home. Later, she learned that she lost the baby.

In Lilo & Stitch, the movie deals with losing loved ones, grief, and feeling lost and confused.
This is most felt in the scene where Lilo talks to Stitch about how her parents died in a car accident. Stitch later admitted that he felt lost.

In Zootopia, the film's creators talk about segregation, racial profiling, and the ridiculous idea that biological differences between races influence behavior, throughout the entire movie. The movie also alludes to how stereotyping is wrong and that we should all work together to reach equality.

In Inside Out, the creators of the movie gave proper attention to Riley's depression. They showed her depression as a real issue, instead of stating that Riley was just an angsty kid. Riley's clothes even represented how she felt.

In Dumbo, the animation deals with separation, animal cruelty and how animals are abused in the entertainment industry. This is most obvious during the scene when Mrs. Jumbo goes berserk when a kid messes with her child, Dumbo.
However, things don't end well for Mrs. Jumbo: she is whipped, choked, chained, locked up in a trailer, and not allowed to see her own child.

In Mulan, the creators of the animated movie deal with themes of misogyny in society. Mulan proves throughout the entire film that a woman's place doesn't have to be in the home. Every single person can be smart, witty, tough, and capable, no matter their gender.

In Moana, one of the most bittersweet ideas is that the loved ones that we lose are never truly gone—they'll always be with you. This is best shown in the scene when Grandma Tala, who is dying, says goodbye to Moana.

In Big Hero 6, the focus of the story isn't just about relocation—it's the heavy loss of a beloved family member and the grief that comes with it.
Baymax, who is a healthcare robot, sees that Hiro is grieving and helps him cope by helping him reconnect with his friends and the outside world. (Lots of hugs help, too!) The movie also deals with mental health, abandonment, and the theme of revenge.

In Finding Dory, the creators of the movie deal with the topic of being someone who is neuroatypical through Dory's character.
The film showed that it's alright to be neuroatypical, that you're not less of a person, and that people with intellectual disabilities can lead happy lives, just as Dory was able to find her parents.

In Finding Nemo, Disney and Pixar talk to the audience about the topic of love and losing those closest to you. Dad Marlin and his baby son Nemo were the only ones who survived the barracuda attack. Marlin lost his wife and all of his other children.

In Beauty and the Beast, Disney tackles the very serious topics of sexual harassment, sexism, social shunning and male entitlement. Nearly every scene with Gaston and Belle in it shows his ungentlemanly and demeaning attitude toward her.

In Brave, the creators deal with the serious topics of sexism, forced gender roles, and the expectations that the patriarchy has of young women throughout the entire film.

In The Hunchback of Notre Dame, Disney deals with lots of dark themes, including bullying others because they're different, ableism, racism, sexism and sexual harassment, poverty, genocide, and corruption.
One of the most powerful and darkest scenes is when the crowd bullies Quasimodo, throws tomatoes at him, and ties him up because he looked different.

In A Bug's Life, the topics of authoritarianism, fascism, dictatorships, and government corruption are discussed throughout. Some also interpret the movie to have some overt references to Nazism.

In Monsters, Inc., one of the most serious topics is learning how to say goodbye to those that you love the most. It's perfectly encapsulated in the scene when Sulley hugs Boo goodbye and leaves through the closet.
Some other serious themes peppered throughout the film deal with corruption and capitalism.

In Toy Story 2, the movie deals with abandonment issues and the idea that just because somebody was abandoned doesn't make them incapable of love.
In the animation, we learn more about Jessie's backstory, specifically that she was abandoned. However, this doesn't mean that was was no longer able to give or receive love. What's more, this didn't make Jessie less deserving of being loved.

In The Lion King, the animated movie touches upon the topic of how power corrupts and how the desire for power can lead to awful things, even tearing families apart.
This is shown especially vividly when Scar kills Mufasa and then blames it on baby Simba.

In Frozen, the difficulties and challenges of building a healthy relationship with your siblings are analyzed, not just the positives.
The movie addresses how you have to come face to face with pain, ambivalence, jealousy, rivalry, and sometimes even hate if you want to create a compassionate relationship with your sibling.

In Hercules, the themes of sexism and sexual harassment are featured in the movie.
These two topics are addressed through Meg's character who in one scene says that men think that 'no' means 'yes' and 'get lost' means 'take me.'

In Coco, the characters deal with the serious topics of friendship and betrayal.
The scene that teaches the audience about these two themes is the one where Ernesto reveals that he poisoned Héctor,

In Pocahontas, the film's creators address the serious and dark themes of racism, as well as colonialism and its negative effects.
These two themes can be seen throughout the movie.

In Toy Story 3, the movie deals with the theme of how each and every one of us eventually outgrows our pasts and how that's a good thing.
The scene which captures the essence of this is the one where Andy gives all of his favorite toys to Bonnie.
What's more, Toy Story 3 also deals with themes of authoritarianism, just like A Bug's Life.

In Tarzan, the characters deal with the topic of finding hope even though they suffered losses that seem insurmountable and impossible to get over.
The scene that illustrates this best is the one where Tarzan rescues his loved ones and finds home in the family that he chose.

In Cinderella, the creators of the animated movie tackle the topics of losing a parent, parental neglect, and how far from everyone comes from a happy, loving home. One of the darkest scenes is when Cinderella's evil stepsisters tear off her homemade dress.

In Aladdin, one of the main serious topics is extreme poverty, never having enough food, and the desire to live better.
In fact, you could say that if Aladdin didn't live in poverty, the entire plot of the movie (or its sequels) would never have happened.
Some of the other main serious themes were corruption, greed, slavery, and patriarchy.

In The Rescuers Down Under, the film's creators address the themes of environmental preservation and protecting endangered species. They also tackle the topic of illegal poaching.

In Bolt, a couple of more serious topics that can be found between the lines are related to lying and treating animals right.
If Bolt never believed that he had superpowers, the entire plot of the movie would never have happened and there would be no need for the film in the first place.

In The Princess and the Frog, the topic of accepting your fate, however bad it might be, is shown to the audience.
Ray the Firefly accepts his fate, knowing that something good would come from having stolen the trinket and having fought off Facilier's demons. Ray then peacefully passes away, surrounded by his friends.

In Cars 2, the story throughout the entire movie talks about climate change, nature, and the effects that oil has on the world.

In Oliver & Company, the movie deals with the serious topic of living and surviving in extreme poverty.

In Tangled and Cinderella (and partially in Frozen), the topic of parental abuse and neglect is addressed. However, not everyone agrees with this interpretation.