Clarify your main theme. Your book title should indicate the main point, theme or purpose of your book. Figure out what your poems are primarily about and be sure that your title indicates this.
Don't be too obvious. Although your title should clearly indicate your theme, you do not need to simply say what happens in your book. For example, a title such as "Poems About Puppies" is too obvious, as is "All About Puppies." Try to imply your overall theme but not state it directly (Reference 1).
Aim for a short title (References 1 and 2). Since this is a children's poetry book, you do not want to turn off a young reader or a parent by making your title seem too obscure or too adult.
Use a play on words or rhyme. Since you are writing poetry, wordplay is a fun way to prepare the reader for the poetry experience. In addition, a rhyming title can also prepare your reader for the rhyming to come in your poetry. For example, Dr. Seuss titles, such as "The Cat in the Hat" and "Hop on Pop" use rhyme and playful language to engage young readers (Reference 1).
Match the tone of your book to the tone of your title (Reference 1). If your book is playful and fun, make sure that your title reflects this. If your book covers more serious issues, then be sure that your title does not imply a fun, light read.
Check to see if your title has already been taken (Reference 2). Use a search engine to determine if your title, or a title very similar to your own, has already been taken. This is important, as you want to avoid having to change your title at the last minute.