[notice] child pid 1256 exit signal Bus error (10) ????

It means that the child process #1256 crashed while processing a request from a client.

This is most often caused by a CGI or other script that's badly written. Apache, generally, is very stable, and problems like these almost always come down to plug-ins and scripts. The issue, of course, is determining the request that triggered the crash.

If your machine isn't too busy, you might try to cross-reference the access and error logs to see if you can identify the request, either by timestamp, result code or similar. Once you find what's causing the crash you can take steps to fix it.