While I agree that the parks in Rio are generally dangerous based on a lot of reported crime, the parks in Sao Paulo are quite another thing. I think the reason for so little crime around the Sao Paulo parks might be due to many hourly hotels within steps of many parks.
Hourly hotels are cheap. They run between 20 - 30 reais for one hour. The personnel at the hotel keeps the I D of the garoto until you both leave. Most hotels are locked after you are assigned a room, which means that if a garoto caused a problem, the garoto would have a problem leaving the hotel. Furthermore, the garoto would forever be forbidden to return to the hotel with future clients.
For example, Trionon park, on Avenida Paulista, is in one of the nicest streets in the city. The park is heavily patrolled by police (prostitution is not illegal in Brazil) and it is easy to meet garotos there during most parts of the day. On occasion, a policeman offers his services to interested park visitors if there are not many people in the park.
Another park that is nice (but not as nice as Trionon Park) is Ibirapuera Park where there is a nightly parade of hustlers similar to what one would find in Sao Paulo's only hustler bar, Bar Fama.
I have never heard of anyone getting mugged in parks or at Bar Fama.
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