Playground sand is basically a giant litter box used by every bird and animal in the area, and they all have pathogens in addition to other lovely forms of zoonotic diseases and parasites. They are so tiny and microscopic in size that they pass right through the skin on contact, it doesn't have to enter through the mouth or an open wound, and it's practically an instantaneous infection for those with thinner skin, such as younger and elderly persons. 

Can the pathogens be prevented or removed? Nope, not really in a practical sense for most playgrounds. How many outdoor playgrounds with sand you've seen are covered when not in use? How about seeing playground sand removed and replaced every two years? Probably none, in response to both. Kids can also end up leaving pathogens behind, in many ways.

To put thing into perspective, once pathogens are present in sand, they multiply and spread so much quicker when the sand is moist and warm. It no longeer matters if you rake and remove some pet waste, it's already infected or infested the sand. The only manner to prevent transmission is to not have any skin contact with the playground sand at any time, because even using an alcohol wipe afterward won't remove what's already gotten inside of you. 

So, stilll feel good about playground sand? Ah, there's more, and it's not good news. If there are other surfaces such as Pour-in-Place (PIP) alongside the sand, they both share their microbes and pathogens, because PIP is basically a giant unsafe petri dish normally containing salmonella, streptococcus, staphylococcus and other lovely diseases and pathogens.