The first book in this series, “A Wrinkle in Time,” was recognizably science fiction.
There were certainly many fantastical elements, but it was understood in the book that these were covers, cloaks over higher truths. It’s mentioned at one point that the three otherworldly ladies at the center of the novel are “just playing at being witches.”
The second book was arguably even more scifi. Aliens abounded, people traveled into the microscopic level of the human body. Again, the fantastic was knitted through, but the strong implication of this novel in particular was that the universe is fundamentally a place of order. Hierarchies and knowledge were organized, choices were made along previously demarcated paths (although there was power in seeing how to step off the path).
The third book was a time travel adventure, and the science elements got a bit more…fuzzy. For instance, while Mr. and Mrs. Murray’s research had been a huge part of the plots of the first two books, it’s barely mentioned here. Meg and Charles Wallace maintain a psychic connection through the book. And the fate of the world hinges on who the descendants of ancient Welsh kings have babies with. Also, it’s worth mentioning that Charles Wallace spends the novel flying around on a unicorn with wings.
By the fourth book, the science element was approaching total breakdown. Angels wandered around turning into mosquitoes and camels. Unicorns appeared, but they disappeared if you stopped believing in them. Noah and his family were clearly pre-homo sapien, a nice touch–but Noah was having face to face conversations with God, and there’s no way 4 related couples could repopulate the planet. The twins were delivered to Noah’s time by essentially typing in a magic box.
The fifth book seemed like it might go back towards scifi–it was another time travel adventure, and the Murray parents returned–but really it was entirely fantasy. Whereas in the early book an alien would arrive and explain why something was happening, the time travel in this book remained essentially unsystematized and unexplained. The reasons behind events were never fully revealed. A lot of time and worry is spent on how to make it rain in prehistoric New England. And random ancient people can perform psychic healing.