No one really intends to create an unsafe play area, yet it's what happens if a particular playground surface like sand is chosen, without fully understanding the associated risks, liabilities, maintenance requirements and costs. Local pets, birds and feral animals see playground sand as a great place to leave their waste. If there's any moisture within the sand, then it's really become a microbial habitat, spreading mold, mildew, fungus, bacteria, other pathogens, zoonotic elements and parasites. It's sort of like asking your children to play in the cat's litter box, except this one has stuff from birds and wild animals that can be far more hazardous. 

Hopefully, more people will realize there's really no good way to prevent playground sand from becoming infected and infested with nasty and harmful contents, that really cannot be eradicated effectively. There are even some playgrounds with sand that have bacteria that's resistant to and can't be treated with antibiotics. 

The only way to mitigate the problems with sand in a play area is within a smaller sandbox, that can be covered with not in use, and even then it can still become a microbial habitat, when something finds its way in. Remember Jeff Goldblum's line in the Jurassic Park movie, "Nature will find a way?"