2 Days in Swiss for Late November 24

The train from Luzern to Interlaken is more properly the Luzern-Interlaken Express. It is a section of the Golden Pass train route.

4-5 hours to do the Rigi Kulm by boat is about right.

No idea about First Cliff, only it will be a day of mostly riding trains and lifts.

Instead of First Cliff, any good recommendation for 4-5 hours from Interlaken?

Or any good day trip from Lucerne?

The First Cable Car is closed until November 30 for "revision work" according to this website https://www.jungfrau.ch/en-gb/live/operating-info/.

So much is weather dependent. Perhaps go to Grindelwald or Lauterbrunnen and ride the mountain cogwheel train to Kleine Scheidegg? Or from Grindelwald, take the Eiger Express Cable Car to Eigergletscher, which is quite high up on the mountain. With clear weather the scenery is quite spectacular. You can ride the Eiger Express up then take trains down stopping at Kleine Scheidegg ,Wengen, and Lauterbrunnen. A lot of train time, but a good way to see the scenery.

A good day trip from Luzern is to take a train to Engelberg, as it is only about 45 minutes. If you want, you could take a cable car to Mt Titlis. It will reopen on November 15.
https://www.titlis.ch/en

For a more scenic train ride to Milan, take the IR26 train from Luzern at either 9:18 am or 11:18 am. Change trains at Cadenazzo to the RE 80 to Milan. These trains do not have required seat reservations with a Eurail pass. The IR26 is called the Treno Gottardo and goes mostly over the mountains and avoids the Gotthard Base Tunnel, which is 30 miles long and goes completely under the mountains.

Firstly, pay attention to the spelling of places. There is no Lucrene, Interlekan or Grinderland in Switzerland.

Secondly there isn't much to do in Grindelwald in late November. A lot will be closed, as its out of season. First is closed for example. Just spend more time around Luzern, eg. going to the Transport museum.

We were in Lucerne a few years ago and didn't bother going to the Bernese Oberland region then.

We did do a day trip up to Mt. Titlis and it was spectacular. The scenery was incredible, and the first time that my husband and son had seen snow.

That would be a much easier trip than the long journey to Interlaken and Grindelwald with such young children.

From memory there was a snow park at Titlis for them to play in.

Mt Rigi is a good half day trip. It should be snow covered. The boat ride and cogwheel train make the trip a nice adventure. Pack snacks, as the food at the top is expensive and not great. If you get a clear day, it will be spectacular above the tree line and clouds.
Zurich main train station has the largest indoor Xmas market in Europe - check the date it opens.
Have a great trip!