It's kind of like the kind of joke a young child would write. It's not very funny, and the whole book is based around it, which is just bizarre. Maybe a young child would find it funny, but I don't. It's not bad, but it's not great. Contrary to the quote on the back by Parenting Magazine, I don't think it will make children eat their vegetables. It might actually make them sympathize with them, which would be the opposite of your intention.
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Eat your dinner so you can get dessert. Or, peas are just like people.