Our Missing Hearts by Celeste Ng

 The setting is a dystopian America in the not-too-distant future. After The Crisis (a violent time of economic catastrophe for most citizens, blamed on China), the government institutes The PACT, which allows the government to take children away from families deemed unsuitable, subversive, unfit. And there really doesn't have to be much evidence.

Margaret and Ethan are happily married and the parents of a beloved son, Bird. Ethan is a professor. Margaret is an Asian-American poet who had published a small book of poetry called Our Missing Hearts. Unfortunately for her, protesters against The PACT have started using quotes from her book in their protests. She and Ethan can see that this might lead to them losing Bird, so Margaret takes off, leaving her heartbroken husband and son behind. Three years later, Bird decides to go and find his mother.

It's a very sad, beautifully written book.