Here's a youtube video of a walk from Pienza to the Cappella Vitaleta. You can judge for yourself if the streets seem too bumpy or steep.

San Quirico isn't particularly steep. There's a nice park but I'm not sure if the paths are smooth.
The outlets ought to be easy.
Walking through a group of cypress trees with a pram doesn't sound easy to me. Do you have any other means of transporting the child? Back or front pack? Prams are better suited, at least in my experience, to cities and sidewalks, and not country roads, woods, or ancient hill towns.
I'll be you can find videos for each of your destinations.

As i read people have trouble with orams in tuscany it seems it is not the right destination. We usually go to swiss alps and austrian alps villages with a pram so i find it strange the infrastructure is not good in Tuscany enough.
i tried to fill only two days around Pienza bat with a prams seems pointless.
thanks anyway

First of all you are hiring a car so you can revise your program as you go along.

Second, many in Italy do use prams but you must undestand that Tuscan hill towns are very attractive. Not necessarily best suited for prams - Certona is a good example. However, you do not state the age of your child. Is permanently in a pram? Can be carried? Can walk a bit? When you talk about infrastructure in Tuscany as not being good enough what exactly do you mean?

Finally, you also refer to a problem with uphill walks. Does this refer to your child or yourself? More clarity could allow Fodorites to suggest more suitable locations. I have two children who spent many of their early years visiting Tuscany and never had problems if you choose destinations relative to their age.

I'm not sure of the definition of a pram. I imagine a big, heavy, conveyance such as the one Mary Poppins used. A small, folding, but sturdy, stroller would work in most towns. After all, people in all these towns have babies, although they may not often take them walking in the woods.

With a car, you can visit many places and spend more time in the places where you can get around comfortably.

When we traveled with my little granddaughter, we found a sling very useful, along with a stroller, If the road was too bumpy, one could carry the child, using the sling to distribute the weight, and the other could manage the stroller.

Get a three wheeler, much easier to push on uneven surfaces.

The best all-terrain and 3-wheeler buggies 2018 | madeformums.com

Plenty of time till September to get in shape.

I use a pram simair to this:
https://www.google.co.il/search?q=pr...zA1kjjYRECDOM:

well the kid wil be 7 months old and also i have some knee problem of walking uphill.
However, in swiss and austria i always find the right villages in alps which are not steep and the floor infrastructure is excellent.
i thought of finding some villages which will be easy to handle and to stop with the car next to known places but if whole tuscany is problematic then I surely not going to spend the whole vacation in the car.
i wonder how people in wheelchair get along.
thanks!!

That pram looks as though it can handle uneven ground. My only doubt would be whether it could be carried a short distance if necessary. It might be worth your while to get an inexpensive light-weight stroller just for this trip. Something like this would be useful. It's very lightweight and has a carrying strap, but it also has sturdy wheels.

https://www.amazon.com/dp/B00PX8PDII..._detail_4?th=1

All newer buildings and streets in Italy are built to modern accessibility standards, but for some reason the tourists mostly want to see the 800-year-old buildings on narrow medieval streets. Also, Tuscany is famous for its hill towns, and hills are by definition steep. For your purposes, Pienza is an excellent choice, as it's mostly flat, There are many others. Montalcino is on top of a steep hill, but once you get there, there isn't a lot of climbing. Montepulciano is stretched out on a ridge, and is full of ups and downs. Monteriggioni and Buonconvento are pretty flat. I am not an expert on Tuscany, as I live to the east of there, in Le Marche. I'm sure others can give advice about specific towns. You might also post on TripAdvisor's Tuscany forum, as there are several regular posters there who actually live in Tuscany.

Many, maybe most, small towns in Italy are not friendly to cars, if they don't prohibit them entirely within the walls, In this case, there is parking outside the town. Some larger hill towns (for example, Siena) have elevators or escalators to take you up to the town. (However, Siena is also pretty hilly within the town.) Orvieto has a funicular railway to take you up to the town, but it's also not terribly flat up there.

Lucca is flat once you are in Town.