It likely happens more often than you think. The Desitin tube gets stepped on, or the little one squeezes it for fun and it gets all over the carpet. It's not the end of the world. If you act quickly -- as quickly as possible -- you'll be able to get the Desitin up before the zinc oxide stains the carpet. As you clean, take care not to push the Desitin even further into the carpet fibers where it will be more difficult to remove.
Scoop up most of the Desitin with something stiff and thin. A playing or credit card is ideal. Hold the card at the edge of the blob as close to parallel to the floor as you can get it while keeping its leading edge in contact with the carpet fibers. Then push forward quickly with medium force.
Blot -- don't rub that will simply push the Desitin further into the carpet fibers -- as much residual Desitin as you can with a dry rag. As soon as one part of the cloth is saturated with Desitin, move to a clean part.
Pour baking soda on the remaining Desitin. Leave it for two to three hours to soak up the grease. Then scoop up the saturated baking soda with a stiff card.
Spray the spot with a grease-fighting commercial carpet stain remover according to the manufacturer's instructions. Then blot up the stain and the residual cleaner with a clean towel. Again, move to a fresh section of the towel once you dirty one section.