Hello harnit2010
Thank you for your post.
The best option for you is the Swiss Travel Pass: it is a digital ticket that you can purchase online valid almost everywhere in Switzerland. Here are teh details: Swiss Travel Pass – the All-in-one-Ticket for Switzerland | SBB
With this option you have many advantages, among other that your kind can travel for free with you.
You can download the Swiss Travel Guide App | SBB to be sure not to miss any highlights and the SBB Mobile App to be always informed about timetables.
If you decide not to buy the Swiss Travel Pass, you need to buy regular tickets fo each transfer (except for your child, since he is 5 year old still): the tickets can be purchased via the SBB App.
If you have any more question, please call our SBB Contact Center (0041 848 44 66 88, CHF 0.08/min)
I wish you a nice day
EleonoraS