OpenSSH versions 4.4p1 and up (which should include the latest version with CentOS 5) have SFTP logging capability built in - you just need to configure it.
Find this in your sshd_config (in centos, file /etc/ssh/sshd_config):
Subsystem sftp /usr/libexec/openssh/sftp-server
and change it to:
Subsystem sftp /usr/libexec/openssh/sftp-server -l INFO
INFO is just one level of detail over what you're seeing by default - it provides detailed information regarding file transfers, permission changes, etc. If you need more info, you can adjust the log level accordingly. The various levels (in order of detail) are:
QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3
Anything over VERBOSE is probably more information than you're looking for, but it might be useful.
Finally restart the SSH service to update the changes (centos):
systemctl restart sshd