The children's stealth actions make me think of The Adventures of Tom Sawyer. It is a previous classical novel about children's adventure. Their actions seem naughty but clever, like spitting on the squeaking gate, and grabbing each other's wrist as a ladder. They may imagine themselves as agents of a special force.
They try to see into the house, and they see an ambiguous shadow. It could be Boo Radley himself, his family member, or just an illusion