Did your kids track mud into the house again and stained the carpet. Here is a quick trick to get it out.
First, while the temptation is there to immediately attack it with a damp cloth or sponge, resist! Allow it to dry untouched, although you can carefully lift any larger chunks of dirt or mud.
Once it is COMPLETELY dry, attack the spot by brushing it with a medium-hard-bristled brush to loosen all the dirt from the carpet fibers. Then simply vacuum well over the spot and it should lift all the dislodged mud from the carpet. If any stain remains, repeat the process, then it is time to attack it with a damp cloth or sponge as needed.