There isnt actually a "mushroom patch" There are two things people are referring to. One is an event where you find a mushroom patch according to the dialogue and can either harvest them or let them go. The second is a method of tricking the game. If you see a mushroom, you can pause the game and drop a bunch of kids on it then unpause the game and each kid will pick up the same mushroom and return it for more food. People are starting to call each mushroom a mushroom patch since they can technically carry more than one back from the same mushroom. Each one taken back also adds to your mushroom count.

You cheaters

Some people would debate whether taking advantage of a game glitch is actually cheating since its possible. Who knows hehe but its fun to try.