In this look into a possible future, David Gerrold harks back to Robert A. Heinlein's "Tunnel in the Sky" juvenile novel from the '50s. Instead of using starships, people travel from Earth to other planets by means of gateways. There's an element not found in Heinlein's work: time slips that enable people to start the terraforming process on a planet, slip forward by vast amounts of time, then go back to refine things. Not much time passes on Earth in the meantime.
An unexpected time slip in Linnea's development left humans stranded for 3,000 years. They developed their own society, while plagues helped them forget that they had come from Earth. They aren't nearly as technologically advanced as Earth people, and they are very suspicious of outsiders. The people of Earth, nevertheless, need to colonize Linnea and hope to do this without the Linnean humans being aware that the new people are from another planet.
The narrator, Kaer, is a child of a group marriage. When she's eight years old, her family decides they want to help colonize a new planet and choose Linnea. Kaer is pleased because she's fascinated by the horses, descendants of Earth horses which have grown larger than elephants in Linnea's lighter gravity. After a few years, the family moves into a huge dome environment set up to emulate just about everything about Linnea except the gravity.
There is a lot of exposition of how the Linnean environment in the huge dome is made to work. Kaer, her family, and other prospective settlers absolutely must learn everything they can to fit in on Linnea without arousing suspicion among the natives. Failure could result in execution by the theocratically ruled Linneans. Kaer and her family must not only learn to speak the difficult Linnean language, they must learn to think like Linneans. They also have to abandon just about all modern technology. The training is long and hard. Some families just can't make it work. Kaer's family wants very much to succeed, but at times they question if it will all be worth it.
This is the first book in a trilogy. The second book, Child of Grass, is available, which is a relief because the ending of Child of Earth is somewhat abrupt. Fortunately, you don't have to wait to continue reading Kaer's adventure. I've already started the second book. David Gerrold has done an outstanding job of world-building and I want to see what comes next.