I just found out a subordinate earns 26% more than me, what do I do?

Also, from my experience as both a developer and a manager of developers, there are many fewer people who have the skills to effectively manage a group of developers than there are developers (and they're usually already senior developers before they become managers). Thus, I'd expect that good managers would be harder to find and would thus deserve a market premium in their salaries. Also, when I was a manager, I had a more stressful job (being responsible for the work of many people) and worked longer hours than when I was a developer.

When I became a manager, I had the same experience: I found out that a couple of my reports had higher salaries than I did. I asked for, and received (without argument) a big raise.