In connection to the works you’ve listed in your question, you might think about the ways in which childhood is presented as a form of early independence. In many of the novels, the main characters are orphans or getting by without their parents. For the most part, they don’t have reliable adults that they can depend on. The absence of a stable grownup presence makes them quite independent.

In Homecoming, Dicey’s mom doesn’t die, but she does leave them, which forces her to, more or less, play the role of a parent. In The Secret Garden, Mary’s parents die from a plague. Though Mary is rather spoiled, she showcases her independence by taking the initiative and forcing her cousin to realize that he’s not so sick. Harry Potter, too, has to face life without his mom and dad.

You could also talk about the different ways harm or evil is represented in these works. In most of the stories, childhood is not depicted as a safe space that’s free from danger and adversity. The children and young adults face perilous and, sometimes, lethal forces. Harry Potter has to confront Lord Voldemort, while Mii has to experience the horror of the United States’ atomic bomb attacks on Japan. In January’s Sparrow, Sadie and her family experience the brutal injustices of slavery in the United States.