Rio's public transport

1) No. Your options are a single ticket, a pre-paid metro card or the Riocard, which is supposed to integrate the various forms of transport.

Your best option if you intend on using the metro system a lot is to get a pre-pago and top up at the machines you'll find at each station. You'll save a lot of time in queues. There are a variety of cards, some integrate with other forms of transport which are extensions of the metro system.

2) Children up to five years of age travel free.

3) Rather than reinvent the wheel, let me direct you to that rarest of creatures, a Twit Advisor thread that's actually useful. This is a pretty comprehensive guide to using the metro.

http://www.tripadvisor.com/ShowTopic-g303506-i1199-k5602928-Metro_Rio_Rio_s_Subway_A_Little_Guide-Rio_de_Janeiro_State_of_Rio_de_Janeiro.html

4) Praça Quinze, pra sah kin zee.

Thanks Corisco. You've been a great help.
The link was useful and the author did a good job.
I certainly didn't realise about the weekend line changes and that fares on some bus lines are already included in the metro ticket cost.

Nice info there at that link. Note that the Uruguai station is in fact now operating. Important to pay attention to the women's only car... you'll feel like a dumbass absent-mindedly getting on that and getting told to get off by the station guard (yes... I did).

Yes, that link is a year or so old but it is a pretty good guide. Uruguai opened about three months ago. Not that I suspect too many tourists will be heading beyond or even to Tijuca. Someone really should do one for the train system but again not too many tourists use the train. That said, judging by some of the far flung places people seem to have booked accomodation in forvthe World Cup, I suspect a few more will be enjoying the experience.