Final answer:
The children in 'To Kill a Mockingbird' sneak out to check on their father, Atticus, who is at the jail with Tom Robinson, due to concerns for his safety amidst potential mob action.
Step-by-step explanation:
In To Kill a Mockingbird chapter 15, the children sneak out of the house late at night because they are concerned about the safety of their father, Atticus, who is guarding Tom Robinson at the jail. There is tension in the town over Robinson's trial, and Atticus is facing a mob that wants to take justice into its own hands. The children's motivation is driven by a mixture of fear, curiosity, and a strong sense of loyalty to their father.