Really awesome work--not a surprise coming from you--I like it!
If you were going to twist my arm for a crit I might say that the piece tends toward the "cold" and as a children's piece you may want it warmer. Or you may not--like I said, it is really great.
If you were going warmer you could bring in more orange light. Alternatively (or perhaps along with the orange) you could bring in more whimsical pink/magenta tones into the clouds.
EDIT: I've pinned the first illustration of Helmet & Hound you did under my "Best Children's Illustrations" board (just wanted to let you know in case you wanted to put that in your resume lol). Keep us posted if you do a H&H book. Those images look amazing.