This is kind of obvious, but why isn’t there a web part for showing subsites?
Sure, there is the ‘Table of Contents’ web part, but annoyingly that shows other things in the site, like lists and libraries, rather than just child sites. And there isn’t any setting I can find on it to make it behave that way – which also seems a pretty obvious feature. So annoying – 90% there, but not quite.
Well Chis Johnson has has the same though and made an example. I’m not entirely convinced about creating the output string in the property (that’s a bit bizarre Chris), but it’s a good start.