>>If we plan to spend the last day at zurich which panoramic train is best from lucerne?
There are no panoramic trains between Luzern and Zürich, unless you want to take a very circuitous route incorporating part of the Glacier Express route.
There are some options for taking in some nice scenery though:
Via the Emmental: Luzern/Lucerne to Zürich via Trubschachen (2.5 hrs)
This takes you through the picturesque Emmental (the Emme Valley, from where Emmental cheese originates). This is an area of rolling hills with plenty of traditional buildings to be seen.
Via the Zugersee (Lake Zug): Luzern to Zürich via Arth-Goldau (1.5 to 1.75 hrs)
On this route, the train travels high along a hillside on the eastern side of the Zugersee, and you have scenic views down to to the lake, lakeside villages, and the mountains (including the Rigi) on the other side of the lake. Sit on the left.
For comparison, the fastest way (which the Swiss Timetable will bring up by default) takes 45 mins to 1 hr.
These trips can be planned using the Swiss Timetable:
Should you wish to incorporate the Glacier Express route, you would be in for a much longer day (6.0 to 6.5 hrs). To get this route in the timetable, you put in From Luzern To Zürich HB (Zürich main station) via Andermatt and via Chur.
If your trip includes the Glacier Express train between Andermatt and Chur (shown in the timetable as GEX), reservations are obligatory. If you are happy to carry your child on your lap the whole time, you don't need to make a reservation for them, but if you would like the option of using an extra seat, you would also need to make a reservation for the baby. Reservations can be made here up to 90 days before your travel date:
If you take regional trains along the same route, reservations are not required.
>> And is it still possible to take the rhine falls?
You can decide this for yourself by using the Swiss Timetable to see how long it will take you to travel there and back. It's also a personal choice how long you want to spend there. Some people might be happy with an hour, others might like to spend the best part of the day there doing boat trips etc.
This page will tell you how to get there and other tabs provide additional information:
I have attached maps showing the routes mentioned above.