The post The Whole Library Approach (American Libraries, June 2013), focuses on the importance of all staff members, not just those in the Children’s Department, being able to serve children. By extension, staff should be able to fill in for each other in other departments. Though I will stop short of suggesting that everyone should be able to do everyone else’s job, I will say that by using cross-training, you should be able to ensure that operations don’t come to a stand-still in any area just because the usual staffer is unavailable for any reason.
The Whole Library Approach has some great suggestions to provide staff training in areas other than their assigned ones. You’ll also want to see The Importance of a Whole Library Approach, a YALSA Issue Paper on the topic.