Author/agent Mandy Hubbard wrote an interesting post earlier this months on trends in publishing. She specifically talks about young adult and middle grade, touching on picture books.
You might like to check it out here.
The professionals can work up their charts, but who knows when a book will come out that captures the public's imagination *coughstephaniemeyercough*? That kind of response is hard to anticipate.
There probably not much point in trying to write something to meet trends because it takes so long to get something out in book form anything trending now could be dead by the time yours comes out.
Besides, is just meeting a trend why you write? What's your motivation?