3 Days in dolomites with 2.5yo son, suggested itinerary please.

Will you have a child carrier backpack for your son?

Baby carriers. Nope i wont.

HI,

I stayed in Ortisei last summer and loved it. I stayed at the Casa Al Sol...it belonged to the Val Gardena association and so I was able to go on guided free hiking tours on two of the days that I was there, we simply tipped the guide at the end of the day!....he took us up in the cable car(s) which are located within walking in town and from there we walked for a few hours before stopping at a rifugio for a snack/lunch...and continued....

we also were able to use the community pool which was so so nice...it not only had a large indoor pool but an outdoor one, an area for small children and a huge whirlpool as well as a small playground....we were simply required to purchase and wear a swimming cap and to shower before entering. I loved the area and hope to return some day!

thank you, hoping someone could offer an advise.

You can find some excellent suggestions in this book:

https://www.amazon.com/Walking-Italys-Val-Gardena-Dolomites/dp/B0BT6RHGKV/ref=tmm_pap_swatch_0?_encoding=UTF8&qid=1683041915&sr=1-5

You might consider the Val Gardena pass to cover some of the lifts. Also note the opening days for some of these are in June. This pass does not cover the lift from Seis to Alpe di Siusi.

I would not take a 2.5 year old on a chair lift. My heart races thinking about a toddler on the ridge line also. But that’s probably just me.

I still have no idea where to go in Dolomites.

Well, your choice of Ortisei as a base is a good one, because you can make good use of the enclosed lifts to Alpe di Siusi and Seceda (both the funicular and the cable car are worthwhile).
On Alpe di Siusi, you really do not need to walk far to get to some great view points such as this one: https://maps.app.goo.gl/JGRVXD6upH4XDHAw6
With a 2.5 yo in tow, you will only be able to go on very short walks without the appropriate equipment (=carrier). 2.5 is tricky, as children tend to outgrow carriers by then but typically cannot walk that far either.
Walks to the best views are even shorter on the Seceda side - although I would not attempt to go to Pieralongia and back with a 2.5 yo, it's about 1 hr each way and not that flat.
As for the church you mention, it is just outside Ortisei. And Adolf Munkel Trail is on the wrong side of the mountains so you cannot easily reach it from Ortisei.

Thank you for the guidance will arrange accordingly.

I rented a shoulder carrier brand 'minimeis G4' specially for the trip. Is there any accessible lake? is there a way to rent a car?

There are car rental offices in Bolzano.

The most noteworthy lake in the area is probably Carezza lake, but that's a one-hour drive from Ortisei. Otherwise, in Ortisei's own valley, you just have a few tiny lakes as far as I know.