where are the travel friendly cities in south america?

South America isn't really a "family destination". Some South American country's are run by oligarchys ... which in South America are called Junta. (I actually learnt something out of history lol!) It means "rule by a few" , e.g mililitia partys. However children can learn alot out of travelling to South America and it would be certainly more educational than Disneyland!

Good luck!

I would say the turistic places are concentrated in the Pacific coast, the andean mountains and the South Atlantic coast (from Rio de Janerio to Buenos Aires)

You should consider each country's capital.

Besides that south america is rich in nature, well known are the Galapagos Islands and Manaus on the Amazon jungle. There are also lot of volcanoes, high altitude lakes, and of course nice beaches.

Buenos Aires.
Beautiful, very European, great affordable hotels and restaurants.
People are friendly and helpful.

South America countries are very different from each other. You have to ask yourself what sort of vacation experience I want. Do you want to visit a modern city with great museums then probably go to Argentina. But if you want to experience history and visit ancient buildings then visit Peru. However, if you want to know which are travel friendly (accomodating for tourists) look for countries that have stable governments at the moment. Don't visit Venezuela or Bolivia.