Hello, my family will be flying from the US to Paris on Sunday, May 6th. After a long layover in CDG, we continue on to Stuttgart to spend the week with friends there, before returning to Paris by ICE train on the 13th. We will be staying at an airbnb in Champs-sur-Marne, so will be using RER A allot to go between Disney and Paris itself. We would like to use the navigo decouverte to get around. My main question is, will that be possible to buy one as we get into Paris Est on a Sunday (no ticket offices open?). I am prepared to use single tickets to get from Paris Est to our airbnb Sunday night, then start using the navigo Monday morning and through the week till we fly out of CDG on Friday. I apologize for this lengthy inquiry, but I have tried to research this out all myself and still can't find clarification on these two main questions: is it possible to buy and load a navigo on that Sunday the 13th in Paris est, or will I have a better chance of buying the cards from CDG on Sunday the 6th, and waiting to load them using a kiosk in Est on the 13th? It will be myself, my husband and our two children travelling (aged 10 and 8). My daughter will be turning 11 while we are there, on the 16th, does this complicate things? Are navigo decouverte available for my children, and if so, are they discounted like childrens carnet tickets, or will they be all the same price? Thank you, so much, for any insight you can offer on this!
Paris Metro / RER ticket windows in Paris Est train station will be open until around 11:30PM so you should be able to purchase Navigo Decouverte cards for yourself and your family on the Sunday of your arrival. Sounds like you already know that you won't be able to use the Navigo cards until Monday morning and that single-use RER tickets or Paris Metro tickets will be required on Sunday evening.
If you have time on Sunday the 6th at CDG Airport train station to buy the Navigo Decouverte cards, you could purchase the cards themselves then, without loading any week subscription onto them (so only 5€ per card itself at this time). Then when you arrive at Paris Est on Sunday you can use either the ticket machines with your PIN protected credit card to load the week pass onto the Navigo cards, or visit the ticket window to have an agent do this for you.
There is no child version of Navigo pass so the cost will be the same regardless of age.