First Words with Peppa is based on the Dolch Sight Words list - the 220 most common words found in children's English-language reading material. Each Storybook introduces around ten Sight Words. These words are repeated regularly throughout the story. It is through this repetition that children become familiar with the words and begin to recognise them. Any words in the story that aren't Sight Words, character names or important nouns, are phonically decodable so that children can use their phonics knowledge to read them.
Mummy Pig's Birthday, a Level 3 Storybook, introduces the following Sight Words: any, could, give, her, just, may, open, take, thank and then.