What makes a good children's picture book?

One thing I've learned through writing and selling is, children just seem to love rhyming books.

Out of 6 picture ebooks I have on Amazon, the two rhyming ones outsell the others by around 3 times!
I think really young ones can pick up on the rhythm, and enjoy the musical feel of a rhyming book. 

Put with simple ideas, thet children can easily relate to, and clear colourful illustrations help make a good picture book.
What do you think makes a good picture book? 

Paula xxx

Here are my two rhyming ones

http://www.amazon.co.uk/Hairy-Spider-Childrens-Picture-ebook/dp/B005HFHI26
http://www.amazon.co.uk/Slippy-Slimy-Childrens-Picture-ebook/dp/B006AV1W9Q