I volunteered for two weeks in Rio de Janeiro in a Child Development project. It was very well organised in my opinion. Felipe picked me up at the airport and dropped me off at the hostel, on our way he explained me how the program worked and showed me a little bit around in the neigboorhood I was going to stay (Santa Teresa and Lapa).
On my first day of the volunteering program I went to the 'school' with an Irish couple. There were around 15 kids that day and throughout the program I saw between 10 and 20 kids every day. The children call it a school, but there are no classes. Our job was to keep the kids occupied in a good way, we played football with the older kids and rope skipping with the younger ones. Afterwards we went back to the school and let them draw or paint (they love painting!)
It was amazing but an advice for future volunteers is: prepare some games, they like to learn new things! And if you can teach them something new, drawing wise or arts and crafts, that would be amazing and it keeps them going for a while. They liked everything we did, but as kids are, they are bored easily so once they were playing for a while or drawing they wanted to do something else. Also, some basic portuguese can come in handy, you can get classes at the program and I suggest you take them! I already knew some Portuguese, but I was definitely not fluent, and people love you if you just try.
Overall I thought it was a very good experience, I learned a lot about Rio, children and myself. I would definitely recommend!
Side note: It was my first time travelling that far away from home and by myself, so I was a little bit stressed at first, but Felipe and everyone in the program immediately made this stress fade away. If you're a first time traveller/volunteer like I was, don't worry, you're in good hands!