(Not gaslighting per se) but Paddington is accused and convicted of a crime he did not do. At first, the 'father figure' also does not believe him (but the rest of the family does) but he eventually come around and believes in Paddington's innocence.
Paddington is a bear child, not a human child, but he does get wrongly convicted of a crime and sent to an adult prison away from his family. Paddington is never physically harmed, but the prison is bleak and lonely, and conditions are poor at first. In context it is not as disturbing as it would be if this happened to a human child, and everything resolves happily.
Paddington gets wrongly convicted of a crime and sent to prison, and there are moments when he gets sad or someone threatens him, but there is no physical abuse.
As mentioned in other comments, there's a scene where Paddington is trapped underwater for a long time and it looks like he will run out of breath. But he is rescued.
In a flashback scene that happened many years ago, there's a circus performer who dies from a fall when someone sabotages her equipment. It's not graphic and wouldn't be too upsetting for most viewers.
The villain is eccentric and talks to himself / other personalities; he is implied to be mentally ill. He is violent towards the family and Paddington.
Not clinical dysmorphia, but there's a man who's somewhat unhappy with the visible signs of his aging, most likely at least partially because he's having a midlife crisis after being passed over for a promotion.
Someone hides in a box not much bigger than her, and the lid is closed. She stays there for a while. We don't see it from her perspective. Someone is imprisoned in a cell of a few square meters, the only window high up.
Spoiler: Nobody actually dies from drowning, but Paddington, for some time, is trapped under water. It is a very emotional, high tension scene but in the end he is saved