Here are some of my go-to resources on writing for children.
Books on Writing
Favourite Picture Books
David Slonim, I Loathe You (a wacky twist on the guess-how-much-I-love-you theme)
Jim Tobin, The Very Inappropriate Word (wickedly funny vocabulary extender)
Winston Churchill, Painting as a Passtime (wonderfully engaging essay by this historical giant about the role painting played in helping him overcome depression. I include it here because he makes the strongest possible case for cultivating engrossing creative interests outside your usual routing, with a side note about the joys of losing yourself in a library for a day. And you can read it in an hour — a well spent hour at that)