Marais to CDG by RER
 

I am checking all our options. We could use the Châtelet - Les Halles RER station to take the train to CDG but does it have an elevator or escalator? I've been looking at the RATP site but having difficulty. I found the Access Aeroports schedule but are these trains express to CDG? Thanks so much.

It has both.

If you catch the RER at Châtelet there are going to be two options to CDG. One train will stop at every stop on the way. The other will stop at Gare du Nord and then it is a straight shot to T1 at CDG. On the platform is a board with the names of the stops on the line. If a light is lit up next to the stop it means it will stop there. Get on the train that only stops at Gare du Nord before CDG.

Thank you Mr. Nuke. Now I would like to figure out how to use the schedule to find out what time we have to catch an express train.

You can get a line B schedule online, but I seriously wouldn't worry about it. RER trains run continuously throughout the day. Go to the platform at any time and you won't be waiting more than 10 minutes.