It was three kids, maybe, and had something to do with crystals? I distinctly remember one moment where one of the kids had to use dark magic to solve a problem, and was scared the other kids would shun ‘em for it.
I think it was like, one of the kids was transported to a magic dimension, and had to just survive in this new one. It had a more serious tone
It was on Netflix sometime in the 2010s but I do not know when
This sounds like it could be The Dragon Prince, originally released on Netflix in 2018. It primarily follows 3 children: an elf named Rayla and two humans named Callum and Ezran. It's not about crystals, but in the first season the story revolves around transporting a crystalline-looking dragon egg.
In this world, humans have no innate magic (unlike elves), and so can only perform magic by using the life force of magical beings. Callum ends up performing dark magic to save his friend's life, which causes strife between them. It also leads to a fever dream sequence which might be what you are thinking of when you talk about a magic dimension.
