Hmmm lots of good advise, my 2 cents:
The basement of the Manor department store in Geneva near the train station has every kind of chocolate for purchase.And I mean EVERY.
My young tots really enjoyed the intercity trains that have a kiddie playground car on them. Scenery, not so much.
They also loved playgrounds. There is a really nice one on the Lake in Montreux, and it is right near you take a boat ride to Chillon, which they enjoyed.
The old town in Geneva has a really fun playground right on top of the hill with a nice view and the longest park bench in the world.(or so they say). It is also right near the cathedrale, where a motivated 6 year old can climb to the top and see the view, and right down the hill on the other side(and the main shopping street, Avenue Rhone) is a Franz-Karl-Weber Toy store, also always popular.
Feeding the swans on the quay in Geneva or Montreux was another highly rated activity, and they liked seeing the Jet d'Eau, with its thunderous outpouring of water.The Geneva Art Museum has lots of knights and armour, if your child is male...
So myself with 2 days would stay one day in Geneva for the above activities(Oh and Manor has a HUGE self-service restaurant not too expensive and great for kids on another floor) and take an Intercity to Montreux and enjoy the lakefront and Chillon. No Chocolate train, too many tourists.
Edited: 3:59 pm, August 02, 2012