Ok maybe not...
But I often listen to kids music stations on pandora with my two kids and this one routinely comes on. I really like it. It's called "imagine" by Jetty Rae (she has a couple albums full of really pretty folksy lullabies and kids songs, many original).
But today as I was listening to this particular song in the car - it struck me that it not only fits for actual kids - but is kinda beautiful and wonderful for big adult kids as well. Like the picture she paints for little children to build in the minds is very much the picture us age players often picture.
Anyways, just wanted to share. Doubtful it is "theme song quality" (too melancholy anyways for one) - but it's worth a listen.
Check it out https://www.youtube.com/watch?v=NZfmBJmpNl4
Here's the track on bandcamp... http://jettyrae.bandcamp.com/track/imagine