The market is huge and saturated with thousands of shitty books. Some are so unbelievably bad.
There are a lot of markets out there filled with crap these days. I've been told that's subjective, though, and only my opinion, so I'm sure I'm just a snob.
The challenges are to find a great illustrator, identify current trends in the market, and of course, write a good story (it might be simple, but it still has to be good and convince both the parents and the child to read it).
On my bucket list of some-day projects because I can illustrate it myself.