This is a children's book, but it isn't just an adventure story.
It has science-fiction; The Drs. Murray, parents of Meg, Charles Wallace and the twins) are scientists who are researching Time and Space. Dr. Murray takes a time trip and so do the kids.
There is also magic; a trio of "witches" shows up--Mrs. Whatsit, Mrs. Who and Mrs. Which, and they take Meg, her brother Charles-Wallace, and their new friend Calvin on an epic adventure.
It's also the story of a family with a deep trouble who nonetheless stay together, the story of a young girl who is just coming into adolescence with all the awkwardness and confusing feelings, and the story of a special little boy who is thought to be retarded by townspeople.
The symbology L'Engel uses is powerful and original; a giant brain who seduces those around it into surrendering their free will as an ultimate dictator; a shadow-like smog around planets that represents the presence of Evil, and a special young boy who is more than a genius; who is "something new" who nonetheless can be tempted to his own destruction by vanity.
Wrinkle in Time has a lot of fertile subjects for discussions between parents and children about good, evil, how we treat each other, and the choices we make. Ms. L'Engel often uses moral themes in her books and this one contains excellent subjects for discussions about kindness, good, evil, God, and being different, and about the destructiveness of gossip.
Wrinke in Time is like the Potter books in that it is about boys and girls in a magical or fantasy setting. It is unlike the Potter books because it does not focus on wizardry as a craft. Instead it presents the universe as full of wonder, and united by a titanic struggle of Good against Evil. Like the Potter books, there are sequels to Wrinkle in Time, and the story of the Murray kids continues. This was hands-down my favorite book as a child. I still have my copy almost 40 years later.