If you know what you are going to say but you haven’t written it yet, you are getting ahead of yourself. Write it first. And before that you may have to immerse yourself in children’s literature and understand it and see what makes it work. It isn’t as easy as it looks. I know people who have been working at it for years.
A picture book takes a different kind of writing from a book that relies on text, even if illustrated. You should know which you are doing. Unless you are an artist, a publisher does not expect you to supply the drawings, but you should know how your text will work with the art.
Go to the library and look at the books currently being published. And ask the children’s librarian which are the perennial favorites. There is also a lot of advice to be found in writers’ magazines and market guides.
If you place your book with a legitimate publisher, the publisher will take care of distribution.