Apache prefork mode MaxRequestsPerChild

It's most likely that the lock-up is happening in a module rather than in Apache itself. Your setup sounds pretty minimal, so I'd suspect mod_jk as the culprit. If limiting MaxRequestsPerChild fixes the problem then I'd say that's an acceptable workaround. It's possible that a bug in the module is only triggered after a long time or many requests, and unless you're really keen on tracking this down then making it go away is probably good enough.

If you want to track it down then the first thing to do is configure CoreDumpDirectory to point to some location that the server user can write to. If you can get the offending process to leave a core file behind then it should help you track down the cause of the problem. You can find some hints on doing this in the Apache Debugging Guide.

The way that we typically think about the HTTP protocol, this shouldn't be an issue.

Modern browsers use keep-alive connections, which can only carry one request at a time; in that sense, using MaxClients 1 ought not have an impact, since each request in those connections is completed before the next starts.

However, that's another thing about modern browsers; they use multiple connections. These days, you might get an html page that requires the loading of 40 other resources; images, javascript, css. It doesn't make much sense from an efficiency perspective to pile them all up single-file to send via one connection; instead, they're split up into a handful connections (each of which is still single-file) to fetch concurrently.

I can't find a good authoritative source of information on each browser's behavior, but what I can find suggests that 6 connections is about normal. This is where the concurrency of your server comes into play; each of those 6 connections can concurrently request a resource, acting as 6 different clients from the server's perspective.