Originally Posted by MSPeconomist

You could also take a day trip by hydrofoil to Colonia, Uraguay. It's a small town with interesting historical buildings and sites, views, an old fort, a modern art museum, good food and wine, etc. This could be very low key and relaxing unless you decide to book yourself on a very early boat.

Mendoza is primarily wine. Is your son old enough to enjoy/appreciate this (and do you allow him to drink even someplace where it's legal and/or he's with you?)?

For the Falls, a visa in advance is required for many passports, including USA, to visit the Brazil side. Does this make sense logistically?

IMO you can easily spend 6-7 days exploring BA and enjoying the PH.