score:2
You can trust taxi drivers in São Paulo. Taxi scams are almost unheard of these days, especially after Uber became popular. Just be sure the taximeter is on and running.
Also, check if your taxi is legitimate. In São Paulo, they are all white with a TAXI sign on top and a red plate, like this:
(But don't worry too much about it, fake taxis are not a thing in São Paulo)
You can also estimate your fare beforehand using Google Maps. The estimate for today goes like this:
If you are taking a taxi, the 99TAXI is a better estimate. 99 is a ride sharing company that works with taxis too, and their fares should be similar to regular taxis.
If you end up being charged a much higher fare than the estimate, or you fell something doesn't add up, just call the police (190). But again, this is unlikely to be needed. Also, remember you don't need to tip in Brazil :-)
As for using public transportation, I advise against it, not because it's not safe, but because for your destination you will need to take a bus, which are not very tourist friendly and you have a kid with you. Metro and trains are much better in that respect.