I could pretend that I did it on purpose: that I skipped The Hidden Witch because this book is newer, maybe as some kind of comment on how commercial fiction, especially for younger readers, is so trope-ridden and bend-over-backward accessible that any reader can jump in anywhere and figure out everything important.
I could. But I shouldn’t: it’s not true. So I won’t.
I did read The Witch Boy
, the first book in this series of graphic novels by Molly Knox Ostertag (who also, apropos of nothing, is the artist of the great Strong Female Protagonist series). But I missed the second one, and maybe got The Midwinter Witch from the library thinking it was the second one. (I had them in the wrong order in my list there, so that’s my excuse.) Whatever: I read book one three years ago, and now I read book three.
There are secret families of magical people – large, extended clans spread across the world, several families, each with slightly different traditions and skills and abilities. As far as we’ve seen, they’re almost entirely good, nurturing people, though, like anyone else, they can be close-minded and unwilling to want change. 
Aster is a boy, and in his family, boys are typically shifters – they transform into animals – and girls are witches, casting spells. In Witch Boy, Aster was able to show that typically does not mean must always be, and was able to start training publicly as a witch.
I think Hidden introduced Ariel, a girl about the same age – maybe ten? I’m not clear how old these kids are, but they feel early-middle-schoolish, just prior to the pairing up and worrying-about-sex years – who has witchy abilities, but was adopted, so her heritage was somewhat unknown. Ariel is now part of the same cluster of kids that learn magic (and maybe other things? there may be a Hogwarts-education issue in this world as well) in a homeschooling environment, along with Aster.
This book is about the runup to the big Midwinter Festival, in which Aster’s family (Vanisen) gathers together for a combination family reunion and competition. The shifters (just the kids, as far as I can see) compete in one contest, the witches in another. And the drama in this book is about whether Aster and Ariel will compete.
Aster wants to compete: wants to be seen as what he is. Ariel is reticent: she’s good at magic, but not good at family, and this is all really new to her. Aster’s mother Holly wants Aster to take a pass this year (for what seem to be mostly not-making-waves reasons) and Ariel to compete (since that would help cement her place in the larger family).
Meanwhile, Ariel is having dreams of a powerful older witch who claims to be a living real relative of hers, and trying to drag her into a very different, much nastier kind of magic.
Who! Will! Win!
This is a YA graphic novel series, so obviously it all turns out fine in the end, with all of the good people hugging and being friendly, and everyone winning to at least some degree. I tend to prefer stories with slightly harder choices, but this is fun and positive and affirming: I expect it, and the whole series, are big confidence-builders for all sorts of kids who are odd in one way or another, particularly those whose oddities run up against the gender norms in their families.
 This has been a series for pre-sex kids so far, so how people pair up isn’t as clear. I’m hoping there are pan-family gatherings at least partially for teens to meet and match with each other, or else each family is going to get really unpleasant genetically.