Solar de uyuni with a two year old

Salar de Uyuni can't be done in one day. You need at least three days. It's high altitude with thin air, high winds and freezing temps. Accommodation is very basic, no heating . Not suitable for a family with a toddler.
If you're desperate you can take a drive from Uyuni to the salt desert and return to Uyuni in one day. Impossible to tell how the little one will feel though. It's a bad idea if you ask a father like myself.

Definitely not doable if commencing in Argentina.

From Uyuni a day trip would be doable if you can find a agency to come up with a plan for you at a decent price.

In regards to doing it with a 2yo. Never had one so cannot fairly comment and trust Fieldgates advice of it's a bad idea.

You can see the Salar de Uyuni in a day. Plenty were day tripping the day I visited to just the salt flats. You will miss the lagunas, geysers and volcanoes on the second and third days though

You can do it in a day, but you'll miss all the best bit-shirts;won't enjoy it as it's rushed; and getting to uyuni will be just as tough for your two year old as the 3 day trip. I would wait a few years to do it justice.

we tock our son when he was 1 year old on the three day tour. no problem whatsoever! just do it. the locals loved the little gringo ans asured us, he was the youngst gringo ever visiting.