Too Preachy? Opinions please.

I just finished my NaNoWriMo novel this past Monday--a 50,000 word book in nineteen days.  One of the beauties of writing a novel so fast, is that it tends to take on a life of its own, often taking you to places you hadn't contemplated when you started.

That's exactly what happened with my NaNo nove, the second in my Tree Boy series.

As Sprout, a boy who was sprouted from a seed (book one), discovers his super powers, his adoptive brother and sister try to convince him to become a super hero (book two). They form the Super Hero and Detective Organization, or SHADO, and they try to dig up acts of service that might require a superhero, or solve crime mysteries so Sprout can step in and "save the day." But he longs to know who he is and why he is here on this earth.

From the onset, I knew this was the protagonist's struggle within the book. But what I didn't really know was his true purpose in being here. By the end of the book, almost like magic, his purpose emerged: He was planted on the earth by the Creators in case mankind grew heartless over time. He would be a catalyst to restore the earth to a point where it was ruled by love of nature and of neighbor, rather than by deviousness.

I liked this purpose as it emerged. but I'm worried that it might be too preachy for a kid's book. I would love some opinions.