You may have “Child process killed” error message in your stuerr.log:

2015-03-31 17:28:24.730 [STDERR] Child process with pid: 21506 was killed by signal: 15, core dump: 0
2015-03-31 20:24:58.729 [STDERR] Child process with pid: 8619 was killed by signal: 15, core dump: 0
2015-03-31 20:40:04.730 [STDERR] Child process with pid: 9648 was killed by signal: 15, core dump: 0
2015-04-01 02:00:35.731 [STDERR] Child process with pid: 9976 was killed by signal: 15, core dump: 0

Don't worry. It is normal. Unused PHP processeses were stoped with SIGTERM by the web server. No further action required.

They are helpful for analyzing when real problem happens.