Tom's Midnight Garden is a children's fantasy novel and is often referred to as a time-slip novel. This means that the novel uses a plot device whereby characters seemingly time travel, and we see this through the protagonist Tom, who travels to various stages of Hatty's life through the midnight garden. The time-slip device was popular in children's novels at the time Phillipa Pearce was writing, which includes the novel Charlotte Sometimes by Penelope Farmer.
This novel is regarded as a classic children's novel, as the theme of childhood is a key element of the text. Tom's Midnight Garden emphasizes the importance of childhood curiosity, friendship and playing outdoors - suggesting that some of these qualities have been lost to an extent in the modern age, where gardens have been replaced with car parks. The novel is depicted as a kind of pastoral idyll, representing the rural beauty that has been destroyed by urbanization and industrialization. This, in turn, represents the innocence and playfulness of childhood. Critics have argued that this text romanticizes the Victorian era, understating the suffering of poorer people during this time in history. It focuses on a rich family, who has a large country home with a beautiful garden. As such, this book arguably doesn't give a full picture of Victorian society.
Through this novel, Phillipa Pearce teaches children that elderly people were once children themselves, and they are still the same person even though they appear different. She does this by introducing Mrs. Bartholomew, an irritable elderly lady who Tom is warned not to disturb. Tom then meets Hatty in the midnight garden, and they become good friends. At the end of the novel, it is then revealed that Mrs. Bartholomew is actually Hatty as an elderly lady, and Tom realizes instantly that she is still the same person. This is represented by the hug he gives her at the end of the novel, which is described by Aunt Gwen: "He ran up to her and they hugged each other as if they had known each other for years and years, instead of only having met for the first time this morning."