The mood of The Watsons Go to Birmingham—1963 begins as light and humorous. As readers become acquainted with this family, it's hard not to chuckle when Byron's self-love results in getting his tongue frozen to the family car's mirror. Later readers can empathize with Momma when she threatens to burn Byron for playing with matches after she has expressly forbidden it. Momma's response to Byron's attempt to chemically straighten his hair will remind readers of times when they defied their own parents' rules:

“Well, Bozo,” she said, flicking a piece of By’s hair out over his left ear and then another piece out over his right one, “maybe you were planning on joining the circus, ’cause you sure do look like an honest-to-God clown now.”

When the family car, nicknamed the Brown Bomber, gets a record player, the entire family piles inside for more than two hours listening to their favorite music.

The initial scenes in the book are humorous, sentimental, and lighthearted. Even when Byron repeatedly gets into trouble for his antics, Momma and Dad deal with him in a way that is both instructive and often comical. The family is tightly bonded and supportive of each other.

The mood shifts dramatically in chapter 14. When the church is bombed and Joey barely escapes, the family immediately abandons their plan to leave Byron with Grandma Sands, and they all drive back to Flint, Michigan. Kenny has a particularly difficult time getting over the devastating things he witnessed at the church while looking for his sister, and it is Byron who eventually counsels him effectively. This change of mood is effective because it conveys how ordinary lives were often shockingly disrupted by heinous acts of evil during the struggle for civil rights in America.

What is the genre of The Watsons Go to Birmingham—1963?

The genre is that of the historical novel.  Curtis sets his tale of civil war strife in Alabama circa 1963 (as indicated in the title) and follows the travails of ten year old Kenny Watson and his African American family (which includes his Momma and Dad, sister Joetta and brother Byron.)  The family travels from the relatively non-racist Flynt, Michigan, to the seat of the country's civil rights struggles, Birmingham, Alabama. 

Just FYI...this novel won multiple awards, including a Newbery Honor and the Coretta Scott King Honor for best novels of the year (1995) for young adults.