Or maybe the two go hand in hand. I'll get back to you on that.
Check out Figuring Out Theme at Routines for Writers in which a writer/blogger struggles with theme.
For what it's worth, I've heard that some (many?) writers aren't aware of theme until after they finished a work. That is definitely the case with me and my early books. I think now that that's probaby a mistake, particularly for children's/YA writers. There are specific themes that help make a book a children's book rather than, say, an adult book that simply has a child main character. Therefore, I think those of us who are truly setting out to write children's books should be working with them.
NOTE: I am posting less because of your more positive family events--weddings and holiday weekends. Plus this year I'm reading a lot of Terry Pratchett's adult books, giving me less reading to post about. I have a little less material.