Decide if you want to only write your children's story about pets or if you intend to both write and illustrate the story yourself. If you are not an illustrator you should look for an artist to assist you in your project. Sites like Elance allow you look for individuals who are willing to take a percentage or royalties from each sale of your book or take a one-time payment, depending on your needs.
Decide on the age group for which you want to write your story because this can affect the structure and size of your book. For example, for toddlers, illustrations take on more importance. The writing for a children's book for this age group is basic. Use a simple premise with a few words. You can easily write a short sentence for each page. Keep in mind that most children's storybooks are between 30 and 50 pages, which means the word count is often fewer than 1,000.
Brainstorm ideas for your story. Use a notebook to write down ideas of possible premises. Observe different types of pets. If you are a parent with a child who has a pet, think about funny moments that your child has had, for example, with teaching a new puppy tricks. You may decide to write a story that parallels the learning process of a toddler and his new puppy.
Create an outline for your story. Sketch out your book's premise, filling in each section of your story with more detail. Decide if you want the pets in the story to behave like real pets, or if you want to anthropomorphize them, adding thought bubbles above their heads.
Choose a page layout design. For example, you might want each page of your storybook to include text or, alternatively, you might prefer that one page has an illustration with the opposite page having text.
Create each page of text in a graphics program or hire someone to do this part of the process for you.