Jan 31, 2013 - 2:33 PM
Bernese Oberland mountain areas are just starting to open up again by mid-May. All of the mountain transports will be running by then.
I recommending spending your 5 days based in Wengen and tour the area from there. If not enough hotels are open in Wengen by then, Grindelwald would be a good option. I usually don't recommend Grindelwald as there are cars, busses, and tourists there but not so much in mid- to end-May. And certainly dramatically better than Interlaken.
I would stay concentrated on the BO, it's too far of a journey to backtrack to Titlis (by Luzerne) from there. You can easily occupy yourselves with wonderful short trips that feature countless things for the little ones to do from either a Wengen or a Grindelwald base. The mountains in this area are more dramatic than those near Luzerne as well, so yet another reason not to backtrack. I have a 35+ page document on the region that describes many of the things to do, transport tips, a section on things to do with kids, etc. It is written from a Wengen base but easily translatable to Grindelwald. Happy to send it to you but need your email address to do so. Send it to me by Private Message if you would like a copy.
After a long flight from the US I would head straight from Zurich to your base destination. Your kids will be exhausted as will you and I don't see how you could possibly enjoy a few hours in Luzerne before heading out to your final destination after all of that. And, as mentioned before, with this short of a trip you should overnight in one base only. The train ride from Zurich airport is 3 - 3.5 hours to either base I mention, then you'll be there and able to relax.