As The Chicago Manual of Style helpfully points out,
2.9 Word spacing—one space or two?
Like most publishers, Chicago advises leaving a single character space, not two spaces, between sentences and after colons used within a sentence (but see 14.121), and this recommendation applies to both the manuscript and the published work.
With appreciation to Melissa Stewart who gave me the kind heads-up, and to Jane Yolen and Mark Teague (for their wonderful "How Do Dinosaurs...?" picture book series) which inspired this blog post's title.
Illustrate and Write On,