1 expert has answered
It's a risk for for anyone who's being watched or preyed upon, yes. It's not just a risk for children, in that sense. However, the chances of a stranger targeting a random child are quite small, statistically.
The bigger question for me is "Why does any stranger need to know where I am at all times?" I don't understand the Four Square phenomenon, personally. I've never felt the need to be the Mayor of Starbucks, therefore showing advertisers what I like to eat, drink and do 24.7. It's not really a game folks. It's pure data collection.
If you're over 18 and choose to share your every move with the world, that's fine. I don't think it makes sense for young people to use it.