Sep 25, 2017 - 9:16 AM
Hello KK and Welcome to MySwissAlps
I wonder if your three nights includes the first and/or last night in Zurich? If so, a night in Lucerne and a visit to Mt. Pilatus would be a great choice. If you have a little longer, then I would certainly recommend travelling via Bern to Interlaken. From Bern station you could stroll through the old town, past a huge clock with animated figures, on to see the bears living near the river (all in a couple of hours).
From Interlaken it is an easy day trip to the Jungfraujoch, which is open all year. The train journey includes some stops, allowing you to disembark and visit the viewing windows in the Eiger - ideal for a young child. At the top, you can safely enjoy the attractions with your son.
Here are some links to help with planning:
Have a great trip!