Please! Help with pass! Itinerary Included

With only 3 full days and a toddler, I'd strongly recommend you simplify some of your itinerary and rework a few things. You're done a ton of big days in a short window of time and with a little one, not much room for them to play or feel like you're not running from one thing to the next. For example, it's not realistic to train all the way from Paris to Interlaken, check in to your hotel and then go back out and train all the way to Thun. Also, doing Pilatus and Luzern as a day trip from Interlaken really isn't necessary when you haven't exhausted all the great things there are to do in the Jungfrau region. You can also better choose activities to all fall under the Berner Oberland Pass, which is going to save you a ton of money.

I'd suggest something like this and with that, the suggested pass option at the end...

August 4
Paris → Interlaken
Walk around town, Harder Kulm for sunset

August 5
With a little one, I'd strongly suggest skipping Jungfraujoch. The train ride up to Jungfraujoch is inside of a mountain in the dark inside a jam packed train, it's cold up at the top in high altitude with no activities or enjoyment for little kids. I've done it with my 1 & 3 year old nephews and it was not a hit. Instead do Schynige Platte, an open air cog train that goes up to epic views with optional ridge hike with lake and mountain views + playground and lovely outdoor area for lunch with alphorn players.

August 6
Lake Day on Lake Thun with boat ride to see castles at Spiez, Oberhofen & Thun + the historic town of Thun (much less crowded than Luzern) OR Lake Brienz + Brienzer Rothorn open air steam train (my young nephews loved this, as they could look out the windows the whole time)

August 7
There is no "city" of Lauterbrunnen to explore. It's one small street with souvenir shops. Walking behind Staubbach Falls isn't worth it and definitely not with a little kid and kids under 4 aren't allowed at Trummelbach Falls.

This is a more family friendly option with better views and flow...
Interlaken > Lauterbrunnen > bus to Stechelberg > cable car to Schilthorn if you want epic expansive alpine views (better than Pilatus) > cable car back Murren > funicular to Allmendhubel alpine playground + outdoor patio lunch > funicular back to Murren > stroller friendly walk down to Gimmelwald (or cable car) > expore Gimmelwald > cable car to Stechelberg > bus to Lauterbrunnen (stop there if you want to explore) > train to interlaken

August 8
Switzerland → Santorini
I would allow more than 2 hours before your flight to account for a missed train connection, etc.

With this itinerary, your cheapest option is Saver Day Passes for August 4th & 8th to get you from Basel to Interlaken and from Interlaken to Geneve-Aeroport. You can purchase them in advance right now for 52 chf for each of those days, which saves you around 37 chf per person for the 2 days. Then get the 3 Day Berner Oberland Pass for August 5-7, which fully covers everything 100% on this itinerary.

The numbers are roughly rounded something like this

Full Fare = 580 chf per person
Half Fare Card + 3 day reduced BO Pass + 1/2 fare supplement fares (Basel, Geneva, Harder Kulm) = 410 chf per person
3 day BO Pass + full fare supplement fares (Basel, Geneva, Harder Kulm) = 403 chf per person
2 Saver Day Passes + 3 day BO Pass + full fare supplement fares (Harder Kulm) = 388 chf per person

If you're set on your itinerary, you're probably better off just doing the Half Fare Card + Saver Day Passes, as you have expensive activities that aren't included in the BO Pass (Jungfraujoch, Eiger Express, Grindelwald First, Pilatus, etc.)

Wow thank you so much for taking the time to help! :) as far as Jungfraujoch we are pretty sold on going and will dress appropriately (we come from the cold tundra!) Great to know that about the falls not allowing children, we will forgo that and switch to what you thought for that day. Do you think skipping Lucerne and going to Lake Oeschinensee would be better?

I gave you my suggestions for what would be better :) There is plenty to see and do with the list of options I gave you without doing a major day trip to Luzern or Oeschinensee amidst your short time there and having to come all the way from Paris and then all the way to Greece. Sticking to the Jungfrau region will give you more time to enjoy where you already are.