Well, to draw cartoon monsters easily, first, think of a basic idea for the monster's look. Maybe start with a cute or funny one. Sketch the outline lightly, then add details like spikes or patterns. Use bright colors to make it stand out.
A theme of growth is also possible. Just as the plants start to change and prepare for the colder months, characters in the story could be growing in different ways. It could be emotional growth, like learning to be more independent, or physical growth in a more metaphorical sense, such as becoming more resilient in the face of upcoming challenges.
You can start with simple shapes for the body and add distinctive features like big eyes or unique horns. Keep the lines smooth and the design not too complicated.
Some examples could be friendly-looking pumpkins with cute expressions or little witches with charming hats. These monsters are designed to be appealing and not too scary for kids.