What sort of age range are you writing for? There are big differences between, say, picture books and YA novels. Money is also completely variable. I have heard that the average advance for a first novel is about £5k, but that's not children's books in particular. Maybe ask on the creative writing board?
Hello. I have a children's rhyming book about Halloween coming out in August. I will not link to the book here (in case people get upset about it getting free publicity) but if you're interested I'm sure Googling my username will yield some results.
Q. How much does your work get changed - is it so much that it doesn't feel like yours any more? A. There were some big changes to the end of my book. This book is a collaboration between a UK company and a US distributor - with regards to the text I was fortunate in having a very supportive team but I did have to completely re-write the ending 3 times and feature certain elements before it was approved for the American market. I was fortunate that I still had wiggle-room. For example one suggestion was to include a "dance-off competition" which I was able to turn in to a fancy-dress contest, and that lead me to dream up what I feel is a better ending than I originally had (now the ending is my favourite part!) I think the thing is not to be so afraid of changes that it puts you off - you can always try to negotiate
I also had no say in the illustration (this may or may not apply to you, depending on the kind of book, but it is normal ... and frustrating for someone who wants everything to be perfect ;))
Q. Are you banned from writing any others / producing anything related? A. Yes, there are variations of my book for different cities/states - they don't want me writing location-based rhymes for a competitor.
Q. How much do they take? What region is 'the deal' in - how much is it worth etc? A. I am not allowed to discuss my contract, but for short, illustrated children's books it's often about 5% of list price to the author and 5% to the illustrator, so if you self-illustrate you get 10%. Do some reading about percentages of "net receipts" which you will want to avoid (to see why, it's useful to read up on what the movie industry calls "Hollywood Accounting").
I've got to rush out the door now (for a 3 year old's birthday party!) but feel free to ask any follow-up questions and I'll do my best to answer them