Does anyone know the title of a 1980s book/series about polymorphs?

Humans are in space. An alien race comes upon them. The aliens are single-celled, single-sexed creatures who can change their shapes and imitate other lifeforms including humans. They imitate them so well, humans do not suspect the aliens are among them. The aliens have three stages they go to in their life. Seedlings are the children and are produced by Houses. Houses produce seedlings as genetic experiments. The seedlings are taught and watched over by Tutors, what Houses turn into when they are tired of producing seedlings and want to do something else with their lives.

To the aliens, the universe is a giant mathematical equation that the Tutors created. When the current equation reaches its end, only the Tutors will survive to go onto the next equation. Everyone else will die.

The series starts with the description of one of the aliens called a child. That is considered an unusual title because it means the seedling was produced for a specific purpose. Early in the book/series, this child crashes a ship into a planet inhabited by humans (not Earth) and causes a chain of events that will lead to the child being locked in a safe in a bank while the child's House decides what to do with it.

Any information on the title or author would be a great help. Thanks!