A great way to explore the city with your friends and family!
Let me tell you this: foursquare is an amazing website - when put to use correctly.
foursquare is a new generation of social networks that allow you to 'check in' (broadcast your location online) to your favourite places, be it the public park, or a local Starbucks. It also lets you leave online 'tips' for the places. These are essentially mini-reviews or, as the name suggests, tips (e.g. "Ask for the secret sauce!" at a burger restaurant).
Whilst it does have some significant security vulnerabilities - mainly the fact that it openly broadcasts your location publicly - foursquare, if used correctly, can become a great way to explore your town or city with your family or friends.
The bottom line, however, is that, unless your child is about 15/16 years old, do not let your child create your own account. My account is my parents as well, and they control it. It could give away your location to pedophiles, etc. although while the government promotes it, most of the internet is not full of rapists that will abduct your children. It's a very stereotypical view.
The pure reason I have rated it on for 11+ is because it is a brilliant way to find potential new restaurants/places of leisure for you and your family!
The Common Sense and Common Sense Media names, associated trademarks and logos, including the Decider Slider and Age Ratings Bugs, are trademarks of Common Sense Media, a 501(c)3 non-profit organization (FEIN 41-2024986).