From
www.sbb.ch, Zürich to Paris. Each way takes 4 hours 30 minutes. Change at Basel. 2nd class.
Children holding a Junior Card, who are accompanied by a parent, travel free on the Swiss section. This appears to be valid for a child up to age 16.
For an adult with a Rail Plus and a halb-tax: CHF 315.50
For an adult paying full price: CHF 341.00
For a child, who has a junior card, and whose parent has a halb-tax and a Rail Plus: CHF 145.00
Total: CHF 801.50
If you fly, you have to take into account the time and cost get to and from the airport. A direct flight from Kloten is about 1 hour 15.