I would definitely echo everything RedPhantom says above... relative to any venture into writing and illustrating for kids.

There are simply so many amazing contemporary children's books out there now... on top of the classics mentioned, like Dr Seus, Richard Scary et al.

If this is an area you're interested in going into, I'd definitely suggest reading as much of the existing range of children's literature as you can, from your local bookshop and library, to guage the existing market and also get inspired generally.

;-)