I believe the very best way to introduce a child to poetry is through Dr. Seuss. It may be that his work is nonsense. And that is what children are all about in their learning process...nonsense.
From there I would go to the library with the child and introduce them to borrowed literature, framed in poetry. Once I learned their style and what talked to them the best I would start building their own library.
Poetry is a wonderful way of communication. Writing simply poetry for your very small child is a balm.