The main source of conflict between young Larry's father and mother is that the former is a drunken ne'er-do-well. This makes Mrs. Delaney all the more determined to ensure that her sons don't grow up to be like their father.
With Sonny, she need have no worries. He's an intelligent, studious boy who never causes her a moment's trouble. But with Larry, it's a different story entirely. Even at such a young age, he's already getting into mischief, regularly playing hooky from school and running around with a bad crowd. To Mrs. Delaney's horror, it seems like Larry is very much a chip off the old block.
That's why she tries to deflect him from his current path by placing a book in his Christmas stocking. In doing so, she hopes that Larry will become more like his well-behaved, studious brother Sonny and less like his drunken rotter of a father.
Unfortunately, things don't go according to plan. When Larry sees the book in his Christmas stocking, he's none too pleased, and so swaps it for the toy gun in Sonny's stocking. When Mrs. Delaney finds out about this, she's immediately plunged into despair; her son is a thief. It seems there's now nothing she can do to stop Larry from growing up to be just like his father.