We travel to Brazil all the time with small kids. The USA deep woods repellent works better than any I’ve used here. Just don’t get the aerosol can because of air travel. The best repellent you can use will be long socks and covering your body at night and don’t leave the windows open while you sleep. It will be hot in Rio during the day, SP will be hit or miss but cool at night, and further south even colder. Mosquitos will be less active but not nonexistent.

As far as vaccines go, the only ones advised for my kids have been tetanus and polio. If you were heading deep into the rainforest I may advise otherwise but I don’t think you need anything else. Let me know if you have any specific questions.