Animorphs was a YA sci-fi series that took the mid-90s Scholastic book fair circuit by storm. Written by K.A. Applegate, the books focus on a group of kids who gain the ability to transform into any animal they touch — but only for two hours, or else they're stuck that way. Naturally, they meet and befriend an alien named Aximili-Esgarrouth-Isthill (or "Ax" for short) who also has this same ability, and recruits them to join his guerilla resistance efforts to stop an invasion by a race of slug-like alien parasites who can crawl into peoples' ears and take over their brains.
Wikipedia informs me that there were 54 books in total in this series, although the latter half was ghostwritten, as tends to happen with these sorts of things. They all sported the same uncanny-valley-bad-90s-CGI-cover art of someone morphing into an animal. I remember being pretty obsessed with the series as a kid, and their quarterly-or-so release schedule was a great way to satisfy my voracity for reading. I don't know how well they actually hold up, but even The Paris Review recently sang their nostalgic praises. And, well, kids fighting against an evil fascist empire that's essentially invisible other than the fact that it hijacks the brains of parents and authority figures is, erm, still a pretty relevant concept. I also hear they dealt pretty well with trauma and complicated moral questions, which I vaguely recall as well. I definitely remember the body horror and food horror and surprising amount of death and violence for a kids' book.
Lucky for all of us, the entire 54-book series is now available as free ebooks. I can't imagine they take that long to read, so maybe they could be a good distraction from the other invisible enemy outside right now.
Animorphs eBooks [Animorphs Forum]