I took a course from a published illustrator on creating picture books. Here is what I remember from the course.
* You need to have complete story first, picture books must be submitted as a completed manuscript (just like novels). The only time when publishers are willing to buy an idea, is for non-fiction (and you still need to have all chapters outlined, and at least first three chapters completed), or from well-established writers.
* You need to have at least 3-4 complete illustrations.
* You need to have the rest of the illustrations sketched out (maybe without color, but general outline of how pictures are supposed to look like on the page).
* The whole thing (the text and the illustrations) have to be put together into a mock book.
* There is a standard number of pages that is used by most publishers for picture books (I think it's about 32 for the picture books, or somewhere in that area). You have to aim to come out close to it.
* Publishers are not interested in series ideas from starting out authors. No matter how great your idea is (and I do think it's great!), they are not interested until you finished, sold and succeeded with your first book.
* You can go about submission in two ways..
1.Go to the library and find books that seem to be similar to what you are thinking about. Write down the publishers that seem to do produce books about families, and look up on their websites guidelines for submitting a manuscript.
2. Look up an agent that works with similar books, and send your mock up to him/her.