Rats, like most wildlife , are everywhere. Just because you dont see them doesnt mean they dont exist. Get over it, they are just as valuable to the ecosystem as any other wildlife. They spread no more or less disease etc than anyhting else.
Rats like to tour, they wander the neighbourhood and may show up once a week or more in your garden, sniffing around, eating what they can and move on...they, like most wildlife are scavengers. Dont leave food laying around and they should just keep moving. So they dig a hole now and again! try and live with wildlife if you can. seeing it doesnt mean you have problems with it. However if it's moved in to your sheds or bins, then just clean them out now and again. As for hygiene for kids, adults etc playing in the garden...they can catch a million and one things...just make sure you all carry out regular handwashing and basic hygiene.
Stop trying to change wildlife, and just enjoy it. Their time on this planet is limited, just like ours.