Hi Harjeet -
Welcome to My Swiss Alps.
May is a good time to visit....I always go in late May to visit the countryside and lower altitude regions. Not so many tourists. Rarely, hotel prices may be lower, but, more importantly, rooms are readily available. In some resort areas, there are "Summer Prices" and
Winter Prices" - especially in ski areas.
The disadvantage of May is that many (but not all) facilities of various kinds..cableways, hotels , restaurants, will be closed in the high altitude regions. The snow has pretty much gone away, so there is not much skiing, but the trails above 1500 or 2000 meters are still blocked by snow. So, as you think about whereto go, keep that in mind and check specific web sites where you have a concern.
Places like Wengen and Mürren are at low enough altitude that the snow will almost certainly be gone there, and definitely near Lauterbrunnen on the valley flloor.
We don't provide itineraries on the forum. We provide a lot of well organized information that can guide you in setting one:
Lots of useful links on this page:
Check out he sections on weather and times to visit.
Where to go? Check:
It is quite easy to navigate all of Switzerland by the excellent public transport network, so, do-it-yourself is no problem....unless you are carrying a ton of luggage and changing locations frequently.
After you have roughed out an itinerary, if you post it here, we'll offer comments and refinements. Plenty of people to help with that. ;-)
I don't comment onrail passes; I leave that for the experts m- the forum moderators know a lot of the details. . It is easier to comment after we see an itinerary. The links on this page will help.
Also, when looking at an itinerary, we find it quite valuable to understands your needs and interests for your visit. How old is your child?
Hiking? Museums and culture? Scenic rail trips? Seeing the high Alps? Playing in snow?
Check Alpenroses post on the latter topic in this thread on July 7.
Any dietary concerns?