Sure there's Bambi's mom and Mufasa getting killed off, but those are purposefully done for drama/story reasons. What scenes from kids movies scarred you for life even though they might not have been trying to?
I have two examples: First is the ending of Who Framed Roger Rabbit? Something about Christopher Lloyd's red "toon eyes" scared the ever loving shit out of 6 year old me, and the subsequent melting didn't help much either. The second is the "death" of the air conditioner in The Brave Little Toaster. Homeboy flips out and basically short circuits himself to death and the scene ends with his charred and his mangled "jaw" hanging all over. Honorable mention to the junkyard scene where "sentient" cars are getting crushed to death one after the other