Nicola Morgan has, quite rightly, suggested that a writer should read widely within the genre they are writing in or for. That is the why to find out what is likely to appeal to publishers. Fair enough.
Now, the little problem. Adults choose books that they believe adults will want to read. Adults also choose books that they believe children will want to read - and should read. I suspect that the selection process for a children's book is very different from that for an adult book. (If you are reading this Nicola please correct me if I am wrong.)
If the rest of you disbelieve me head along to the library shelves and take a look at what is there. Read the blurbs on the dust jackets or on the backs of the endless paperbacks. There will be (a) books about social issues - thinly disguised as stories about other things and (b) formulaic undemanding stories that are crude copies of the genuine article.
Okay, that is an exaggeration of course. There will be other things but much of the shelf space will be taken up with those two things. Adults have the advantage. They can dictate what children will read. The child who wants to read will read it. They will read it because it is there. It is, in their view, not too bad but it could be better too. If they do not have access to 'ordinary adventure stories' it is assumed that they will not miss them. It is assumed that it does not matter that they are missing out on the adult equivalent of the detective story. (The detective story is top of the borrowing choices in our local library and, I suspect, elsewhere.) If, the argument goes, a child is going to read then they should be reading something 'useful', something that is going to teach or give them an issue to think about.
For me, having amassed a considerable collection of children's literature from the 1950's on the exciting thing is to have a child borrow a book from me and then come flying through the door at great speed saying , "Are there any more like this?" Are they learning anything from a straightforward story without didactic or moral undertones? Yes. They are learning to love reading. They are choosing to read.