Hello kaphyang yun
Firstly, welcome to the SBB Community!
The Junior Card is valid with the Tell-Pass provided the Junior Card is accepted by the mountain train, lift or cable car operator.
The Junior Card is not actively mentioned on their website as, so I do assume, they primarily want promoting their Tell-Pass for kids. I had to look-up the tariff document 656.3 to find out about the validity of the Junior Card.
However, I wondered what made you think that the Tell-Pass is worth for your trip?
The Swiss Half Fare Card, with the free Swiss Family Card (equal validity as the Junior Card) might be the better investment, in particular if you travel to other regions of our country.
When you stay in Lucerne in a hotel or official Air BnB, you can get the complimentary public transit pass valid for trains & buses service within zone 10 of the public transit network.
Kind regards,
Roland