The Children's Writers' and Artists' Yearbook
A&C Black
ISBN: 10 0-7136-7711-2
Price - £12.99
If I were to recommend only one book, this is the book I would recommend and I would suggest you buy a copy every year, to get the most up-to-date information. It is probably the most important book, a writer for children in the UK, could possibly own. It contains lists of publishers, agents, societies, in fact everything you need to know about the world of children's publishing.
No, I have not read it from cover-to-cover but I am constantly dipping into it, especially before I submit anything.