How do Cassie and her brothers react to the news of the Berrys being burned in Roll of Thunder, Hear My Cry?

In Chapter 1, Cassie and her brothers are greatly disturbed to hear that men of their congregation have been set on fire.
This incident creates anxiety in itself, but when their father issues them an order not to go to the Wallace store for any reason, the children are, indeed, worried about what changes are occurring in their environment. Of course, this incident foreshadows the main conflict in the narrative; for, later in Chapter 3 when Mr. Avery comes to the Logan home, this same problem is discussed.
When he first arrives, Mr. Avery asks Mrs. Logan if her husband is home because he wants to inform him of a growing problem: "It's...it's them again. They's ridin' t'night." When Mrs. Logan asks why they are "riding," Mr. Avery replies that he does not really know, but as they are aware,

"Anytime they thinks we steppin' outa our place they feels like they gotta stop us. You know what some of 'em done to the Berrys...."

The pretext of the burning of the Berrys was that one of them flirted with a white woman, and the other two relatives tried to defend him.
As the Logan children listen to what Mr. Avery tells their mother, they become frightened, worried that the white men will come after them because they have sabotaged the school bus carrying the white children in retaliation for the driver's veering into the muddy water that splashes onto them. They do not yet understand the greater threat.