I went to Rio for 4 days in November 2010 with my husband and daughters ages 7 and 10. The day before we left for our trip, we decided to hire a tour guide and chose Rafa based on all the positive reviews. We were not disappointed and really enjoyed our one day with him. Touring with young children can be a workout but he did an excellent job. Rafa helped us craft an itinerary that highlighted things of interest for the girls, was flexible with the schedule, responsive to emails, picked us up on time, had his own private vehicle and spoke excellent English. We visited Cristo with him, toured the rain forest, spent some time on Niteroi and ate excellent Brasilian cuisine. The highlight of the trip for us was visiting the indigenous settlement (native Brasilian Indians) off the beach of Niteroi. We learned a lot about how they struggle to maintain their culture and way of life while living among modern communities. In terms of downsides, Rafa is not cheap, but he was in line with other tour guides whom we considered.
As an aside, we rented a 2 bedroom condo in a neighborhood in Ipanema. We didn't encounter anyone who spoke English in the area. Therefore, on the days we didn't tour with Rafa, we had to learn and employ basic Portuguese and sign language at the local bodegas, restaurants and shops. This was great cultural immersion for the whole family.
Suggestion: Food is cheap but consumer goods are unbelievably expensive in Brasil. Try to bring everything you need with you (ie, toiletries, flip flops, towels, sunscreen, hats, portuguese dictionary, etc.). We went on from Rio to visit friends in Sao Paulo and gave them sheets, towels, Christmas ornaments and electronics from the States. All of these things cost the earth in Brasil and so make excellent presents.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC