What is the difference between the two -- we will be traveling with our 13 and 16 year old children. Is 1st class worth the extra price?
2nd Class is 2+2 seating, first class is 2+1, with a little bit extra legroom. No need for first class unless somebody else is paying.
Since you are a group of 4, it is best to grab facing seats (first come first served). See photo: http://www.bahnbilder.de/1200/eine-4er-sitzgruppe-einem-talent2-zug-des-729300.jpg
You sometimes get a small table. Exact details vary between different models of train.
Photo of 1st class for comparison: http://killerwal.com/wp-content/uploads/2014/04/berner_oberland_z%C3%BCrich_bern_thun_sbb_04.jpg
Some of the trains are double-deckers. Photo: https://upload.wikimedia.org/wikipedia/commons/0/00/IC2000_Z%C3%BCrich_-_Luzern.jpg