When it comes to drawing, check out the open-source painting program Tux Paint.
Use the Wacom Tablet preference pane to configure the device’s behavior (for example, you might want to disable the pen’s side button to prevent your child from accidentally pressing it). You can get refurbished tablets for as low as $80 through the company’s online store. Small children often have trouble drawing with a mouse, so invest in a pen tablet such as Wacom’s Does your five-year-old watch in fascination as you work with Photoshop? Encourage your child’s interests by turning your retired Mac into a digital art station.