This is why I let my kids play with dirt
It is entertaining, free and a great sensory activity, but there's one more reason why I encourage my children to play with mud.

They love it. Mud to my kids is like coffee to me. That alone should be enough to let my kids roll around like Peppa Pig in muddy puddles. But my kids also love overusing toilet paper and exploring bright crayons on our walls, both of which I strictly discourage. Dirt, however, is different. Aside from it's sensory and creativity sparking attributes, it can be beneficial to their gut and immune system. That's not me saying it— it's science. And there's even a name for it: the Hygiene Hypothesis. Dr. Josh Axe, author of Eat Dirt and Dr. Maya Shetreat-Klein, author of The Dirt Cure, both write about how the exposure to microbes and pathogens in good old' dirt can boost our immunity more than those expensive elderberry gummy vitamins.
Playing in the mud may have lost popularity over the years, but it's as ancient as it gets when it comes to simple means of toddler entertainment. Once upon a time, children went out to the park or their backyard and baked a delicious, homegrown, non-GMO, and organic mud pie. Parents would send their children off to such reputable culinary schools (a.k.a gardens, patios, parks) and allowed them to engage with the dark mushy material without hesitation. Mud was part of the simple joys of childhood, until we literally washed this tradition away.

Some invisible force in my generation decided that we must stir clear from germs at all costs and sanitize our children's lives into adulthood. No joke, I left the hospital with ten little bottles of Purell™ and a newborn. But the problem was not using them with my newborn. In defense of antibacterial gel, newborns are quite vulnerable. The problem was abusing it into toddlerhood and not realizing that this cleanliness frenzy was giving my children diarrhea. Two stool cultures after (and I am talking about those take-home kits) I was ready to try anything that would wipe away this watery poop horror story out of my life. Turns out this "germ-free" lifestyle, sanitizing and scrubbing every surface, was doing more harm than good. It turns out we got it all wrong. I mean "we", as in the Purell™ generation. The antibacterial gel was only invented in 1988, and everyone before then seemed to reap the benefits from natural exposure to microbes in dirt and dirty things. What happened? Your guess is as good as mine.
Don't get me wrong; I am not suggesting we bring back cholera or hookworm. Maybe these historical epidemics are central to our obsession with cleanliness and our sudden aversion to dirt. However, doctors are noting that we have gone off the deep end, and our immune system has become hyper-sensitized. We fall ill at the sight of pollen!
Hence, playing in the dirt has become my biggest ally in keeping my children from falling victims of the next round of stomach flu. And unlike drinking probiotics, I don't have to ask my kids twice to get them out the door. I am not a doctor and the above stated should not be taken as medical advice. I am just saying dirt has gifted us more happy-go-play-outside days over please-go-away sick days.
(Also, please continue to wash your hands with soap and water after using the bathroom, before eating, changing a diaper, before/after handling food, and yes, after playing in the dirt too.)