Or even here:
http://www.travelogx.com/salvadordebahia
;_)-)
I suggest Salvador de Bahia, known as the African heart of Brazil, because it gives a different perspective on Brazil than Rio does (and is in fact the source for much of Rio's musical and historic heritage which arrived with immigrants from Bahia) and is not much more in travel time than some oft-mentioned destinations closer to Rio by bus. Salvador is very rich culturally, historically and musically--and there is a lot for kids to enjoy. (A kid can actually go into the water, something that s/he can't do on Paqueta. :-)

Although many places in Brazil are worth a longer trip (and many tourists think Brazil simply consists of Rio Carnaval, the Amazon, and tropical beaches), 4-5 days is quite enough to get a good taste of Rio. 10 days is reason enough to get two perspectives on the country from different locations.