"I'm thinking of travelling to Sao Paulo/Rio over easter, arriving on Good Friday and staying for 10 days.”
I am not a big fan of Sao Paulo, mainly a business city, with museums (not of the quality one might expect of a world city of that size, but a good education in Brazilian artists), restaurants and clubs.
I would fly into Rio, spend 4 days or so, and go to Salvador to spend some time exploring the city and that beautiful area of Bahia. Or fly AA directly to Salvador from Miami.

“can you tell me the following over Easter:
- is public transport running if so, reduced timetable or normal?
- Are shops, museums, public attractions open normal hours?”

Many Brazilians travel to visit family or take a beach vacation over such a long weekend holiday. I would be sure to book in advance for wherever you choose to be. On Easter Sunday itself, many things will be closed, but you should be able to find food. Most accomodations include breakfast and have a small refrigerator in the room, so you can stock up at a supermarket. Sunday would be a good day to spend at the beach.

"Finally, I'm travelling with my 2 year old son, is there much for kids out there?"

Explicitly for toddlers, there isn’t too much. Most cities don’t really even have public parks, or any with decent playground equipment, and the type of hands-on science museums known in the US don’t exist either. Of course, any kid that age would probably like the beach, but many have large waves, so you must choose carefully.

In Rio, there is a short ferry ride from Praca XV to Niteroi, with a beautiful view back to Rio. The train up to the Christ statue on Corcovado, and the tram lift up to Sugarloaf might be fun for your child. Get off the paved path on top of Sugarloaf to look for little miko monkeys in the trees. There is a part of the beach in Leblon where many folks with small children go called Baixo Bebe. Rio has a zoo with an interesting walkway over one of the animal enclosures, and on Sunday carioca families go to the Quinta de Boa Vista for outings and to ride the train and other little rides too, and eat hot dogs; for you, there is a small gem of an ethnographic museum with some beautiful objects. Nearby is the Feira de Sao Cristovao with music, crafts and food from the northeast region. Get a taxi driver to take you up into the Tijuca forest to look for troops of spider monkeys along the road, and to see some of the other vista points. Maybe the trolley up to the Santa Teresa neighborhood will be running by then. Visit the colorfully tiled artwork of Escadaria Seleron. Have ice cream, pastry of coffee at the 18th century-looking Confeitaria Colombo.

You could go to Salvador where, in addition to a lively and calm cove at Porto da Barra beach, the historic Pelourinho district has a lot of music, movement and color that a kid would love. On Tuesday night, there is the "becao" festival with music and lots of movement. Take in a show of the Bale Folclorico de Bahia. Eat ice cream at the great shop at the top and then ride the Elevador Lacerda down to the colorful Mercado Modelo to buy souvenirs. Go out to the church at Bonfim to see the church and its weird museum of miracles and then stop in Ribeira for ice cream at the famous shop there. Go (by taxi there AND back, don't walk) to the former sugar plantation/current modern art museum at Solar de Uniao, or to their jazz JAM at MAM. Take a ferry over to one of the calm shallow beaches on rural Itaparica Island. Go to the “piscina” cove near the lighthouse in Itapoa (in the direction of the airport), by bus along all the beaches of the coastline in Salvador, to jpoin all the local kids/families. Take an excursion up to Praia do Forte to see the little exhibition of turtles being saved by the environmental agency and do a whale watch. Take an overnight (or two) trip to lovely Morro do Sao Paulo by ferry-bus-boat (the catamaran can be rough), traveling through the lush interior of the state.

Brazilians are fond of kids and will go out of their way to engage with them.

Have a wonderful trip.