Why are mama and big ma concerned about Cassie in roll of th under?

Mama and Big Ma are concerned about Cassie in "Roll of Thunder, Hear My Cry" because Cassie is a young Black girl living in a racially segregated society where she faces discrimination and danger. They worry about her safety and well-being in a hostile environment where racism is pervasive and can escalate into violence. They understand the challenges she will face growing up as a Black girl and want to protect her as best as they can.