I don't know how many times I've heard the saying, "God made dirt so dirt can't hurt." The argument really doesn't make sense when you actually think about it, though. There are plenty of naturally occurring substances that can hurt, no matter who you feel made them. Even being that I follow gods, not a god, to me it didn't matter that this old adage didn't make any sense, because dirt is still just dirt, and really never hurt anyone-right? My toddlers play in the dirt. I played in the dirt as a kid. I'm sure you did as well. Lots of kids play in the dirt every day. They have for hundreds and hundreds of years, but is dirt really as safe for toddlers as most of us feel it is?
Dirt contains bacteria, and can contain viruses.
Dirt does in fact naturally contain bacteria. However, that's not necessarily a bad thing. A study done in May of 2010 found that breathing in mycobacterium vaccae, one of the common bacteria found to occur in soil, may actually increase your toddler's ability to learn, and help them be more relaxed while doing so. Mice that are regularly exposed to soil were able to master mazes twice as fast and did it with less anxiety.
It is also true that viruses can survive in dirt. However, both viruses and bacteria are found literally everywhere. It's impossible to prevent a toddler from ever encountering germs. Luckily, you don't want to do that anyway. Keeping your child in a sterile environment prevents his or her immune system from having any exposure to everyday germs; as a result, it may actually become weaker. Then when your toddler inevitably does encounter a virus or bacteria, their immune system is unprepared and they get sick, or sicker than they would have.
Dirt can contain worms and other parasites.
Dirt itself is usually relatively harmless, but the feces of animals, and possibly humans, using soil as a bathroom is another story. Some worms need to be ingested, while others only require skin to soil contact. You can reduce the risk of infection in toddlers by having fenced designated play areas. Keep an eye out for animals that may hop the fence so to speak. Sand boxes, especially, should be covered, as cats often mistake them for litter boxes.
Dirt can be contaminated.
Soil can become contaminated in a wide range of ways, including but not limited to past presence of lead paint, treated lumber, automobile repair or storage sites, industrial or commercial activity, chemical spills, garbage disposal, structure fires or the use of pesticides or fertilizers. Areas near roadways or parking lots can also become contaminated from vehicle fluid leaks. It's important that you know the history of the land you let your kids play in. This can be sought out using property records, contacting your local EPA, or even asking neighbors. You can also get soil testing kits for your child's regular play areas. When in public places, watch for tell-tale signs such as visible staining on the surface of the soil.
This isn't to suggest that dirt is dangerous for kids, or safe, but that it can be either. There are steps you can take to tip the scales to always safe, but it's still important to be aware that dirt is capable of hurting.
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Sources:
http://www.businessweek.com/lifestyle/content/healthday/639398.html
http://www.usc.edu/hsc/info/pr/hmm/00-01winter/germs.html
http://www.who.int/wormcontrol/education_materials/lao/en/teacher_eng.pdf
http://cwmi.css.cornell.edu/sourcesandimpacts.pdf
