Some girls and boys didn’t receive the presents they expected yesterday morning, and it wasn’t Santa’s fault. Citing a system overload, UPS announced that a fraction of packages would not arrive on time for Christmas as promised. FedEx also apologized for delays and explained that it had processed more than 275 million packages between Thanksgiving and Christmas. Online retailer Amazon, from whom customers purchased many of the items that did not arrive on time, offered a $20 credit to customers affected by delays. What they really needed was a way to explain to disappointed children why Santa had failed to deliver.