Theoretically it would be possible to visit all the places you mention in day trips from Zurich. But I would never do that, because you would spend a lot of time in trains and not so much at the places you wanted to visit. And you would have to start early in the morning and come back late in the night, may be not the best solution with a 6 year old child.
St. Moritz, Lucerne and Zermatt are fine places; Interlaken is a transport hub for day trips to the different mountain Valleys of Bernese Oberland.
You may go by train from Zurich airport (dp 8.13, 9.13 or 9.47) to St. Moritz (arrival 3 3/4 hrs later), relax there after your overnight flight and spend 2 nights there. Day 3 would be taken by the Glacier Express train ride (9.15 until 16.52, in October, it will get dark 2 hrs later). Day 4 and 5 should be spent at Zermatt, with a transfer from Zermatt to Interlaken in the evening (may be Zermatt dp 16.13 - Interlaken ar 18.28). Day 6 could be ussed for a Jungfraujoch trip (but onlly if the weather is fine) and day 7 for Lucerne and Titlils (again if the weather is fine enough).
I suppose you know that there are glaciers close to St. Moritz (Diavolezza, Morteratsch, etc.), that Gornergrat is in the middle of glaciers and that the pincipal attraction of Jungfraujoch and Titlils are glaciers too. May be it could be a good idea to skip either the mountain with the most expensive acces train (Jungfraujoch) or with the less spectacular glacier panorama (Titlis).
Note that the weather in the Alps is completely unpredictable. It may be sunny and fine and you will enjoy it or it may be so foggy (no view at all, resp only about 10 metres) cold and windy that it doesn't make sense to go to any mountain peak.
Switzerland means not only mountains. There are entirely walled medieval towns, a lot of castles and all kind of fine museums spread over the whole territory. May be you havw a look at http://www.myswitzerland.com/en/home.html and the many links you will find there.
For rail passes consult http://www.swisstravelsystem.ch/en/
Timetables and fares: http://fahrplan.sbb.ch/bin/query.exe/en&HWAI=JS!ajax=yes!&
Hotels:
http://www.booking.com/
http://www.bnb.ch/
http://www.swissbackpackers.ch/
http://www.youthhostel.ch/home.html?&L=1
And as you are father of a young son, may be you are interested in the many atrtractions for kids (and not only for kids):
SWiTZERLAND WITH CHILDREN
As public transport is rather expensive in Switzerland, study carefully the sites about Swiss Pass, Swiss Flexipass and Swiss half fare card: http://www.swisstravelsystem.ch/Tickets.16.0.html?&L=2#s_h_f_c
Check the Swiss Travel System Family Card
The Swiss Travel System Family Card is issued at no cost to parents who wish to take along their children under the age of 16 at no cost. Please note that at least one parent has to travel with the child/ren.
Some ideas:
historic steamboats on Lake Geneva:
http://www.cgn.ch/horaires/pdf/AffA2-ete-10.pdf
http://www.cgn.ch/eng/flotte
Swiss Vapeur Park Le Bouveret:
http://www.swissvapeur.ch/en/index.php
Signal de Bougy:
http://www.parc-aventure.ch/Signal-de-Bougy/
http://www.signaldebougy.ch/
Blonay-Chamby historic railway:
http://www.blonay-chamby.ch/index-en.php
Chillon castle:
http://www.chillon.ch/en/
Gruyeres castle, cheese diary and chocolate factory:
http://www.chateau-gruyeres.ch/e/multimedia/spectacle.html
http://www.la-gruyere.ch/en/navpage-ExcursionsFR-HistSitesFR-120085.html
http://www.lamaisondugruyere.ch/index.php?option=com_content&view=article&id=142&Itemid=56
http://www.lamaisondugruyere.ch/index.php?option=com_content&view=article&id=142&Itemid=56
Chatelard-Emosson (Mont Blanc area):
http://www.chatelard.net/english/pages/descr_e.html
http://en.wikipedia.org/wiki/Emosson
http://www.emosson.ch/PublicEN/default-en.htm
Zermatt-Gornergrat:
http://www.gornergrat.ch/home/index.php
http://www.klein-matterhorn.ch/photos/
http://www.zermatt.ch/en/index.cfm
Entirely walled city of Murten:
http://www.murtentourismus.ch/en/navpage-DestinationsFR-MurtenFR-99305.html
http://www.murtentourismus.ch/en/navpage_list-DestinationsFR-MurtenFR.html
Medieval city of Bern:
http://www.berninfo.com/en/page.cfm/Information
http://www.kleinbahn-gurten.ch/
Swiss Village Park Ballenberg:
http://ballenberg.ch/en/Welcome
Lugano and Swissminiatur:
http://www.lugano-tourism.ch/en/291/default.aspx
http://www.swissminiatur.ch/
Seewen in the Jura close to Basel:
http://www.bundesmuseen.ch/musikautomaten/index.html?lang=en
Rapperswil:
http://www.zuerichsee.ch/en/page.cfm/ExperiencesRZ/FamilyDRZ/1230
http://www.knieskinderzoo.ch/
http://www.zuerichsee.ch/en/page.cfm/SightsRZ
http://www.zuerich.com/en/page.cfm/region_zuerich/region_zuerich_x
Rhine Falls Adventure Park
http://www.rheinfall.ch/Attraktionen/Adventure-Park?lang=en-US
Furka steam train
http://www.furka-bergstrecke.ch/eng/train/timetable.php
You may have a look at
http://www.myswitzerland.com/en/interests/family.html
http://www.takethefamily.com/where/switzerland-family-holidays-and-breaks
http://www.eparenting.co.uk/family_holidays_europe/switzerland.shtml
http://www.reka.ch/en/rekaferien/Pages/default.aspx
http://littletravellers.com/destinations/areas/europe/family-holiday-switzerland/