Your child is transitioning from human to centaur. There's no point arguing that species is biologically determined. The child feels centaur and thus is. Accept and validate the child's identity. Dr. Pinder Chipps, a therapist and happy father of two centaurs, can show you how with his book endorsed by Star Trek's George Takei.
The mysterious blogger Obvious Plant creates highly realistic signs and leaves them in stores. As a result, he offers you funny but fake product reviews and extremely specific but helpful bookstore sections. In his most recent prank, he created book jackets for self-help books on basic adult life skills, human sacrifice, and the experience of parenting a new centaur. You can find them all here.