All of these places are reasonably easy to access, and have good accommodations nearby. That being said, they are not Niagara Falls, so some walking (not hiking) will be required. Many of the places will not be stroller friendly, so you might consider a form of baby sling for older children, which will facilitate hauling your youngster over obstacles.
All the sites are incredible, so even if your child may not remember them much when she grows up, there will always be the photographs.
My advice? Do it. Access the web sites, which will help you plan the trip. The Argentine Tourist Board has an excellent site, and they also have overseas offices that you may be able to contact by phone or in person.
http://www.turismo.gov.ar/
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