I wanted to thank you for your timely response to my earlier question about Navigo decouverte for children...it is such a huge relief to know the ticket offices will be open for us on Sunday when we travel! I sincerely appreciate your help. If I may, I would like to ask your advice on one more thing- from Paris est, our airbnb host advised us to take the metro to Châtelet les Halles where we need to switch to RER A to noisy champs. With needing to use paper tickets that evening to get to the airbnb, do we get one to ride the metro then buy a different one for the RER? Or will the tickets in a carnet work the same for both trains? If yes, do we each need two since we will be changing? I think I may have confused myself with something I read about having 1.5 hours to complete a journey on a single ticket. Again thanks so much for taking the time to help, it's truly appreciated!
Single-use RER tickets from Paris-Est to Noisy Champs for each of you I think will be the best option for Sunday evening, rather than a carnet of 10. These RER tickets are specifically priced for that particular journey (Paris-Est to Noisy Champs) so unless you need exactly 10 tickets for that specific trip, it's generally better just to buy one-off tickets.
In either case you would use those RER tickets for the entire trip between Paris-Est and Noisy Champs, for both Paris Metro and RER. Just keep the ticket and use it to pass through any additional turnstiles/gates you may encounter during transfers in Chatelet Les Halles, and to exit past gates when you arrive at Noisy Champs (if there are any).
Have a great trip!