My 14 mo old had staph on her buttocks. What would cause this?

Common issue. The kid likely picked up staph on her hands prowling around the house & touching contaminated surfaces.She then scratched he buttochs at some point and transferred the germ to the break in the skin created by scratching.It could also ba at an inflamed hair root, or bite.These are quite common.
14 months old infect. Any break in the skin can cause that.An insect bite, an abrasion etc can introduce the bacteria under the babies skin.