Our family just returned from a week in Paris, and, for the most part, it was an excellent trip. It had a rough start, though, with our first RER/Metro ride from CDG to our apartment in Jules Joffrin. I want to say first of all that we are not inexperienced travelers or naive about cities. We have traveled in many major cities in Europe and Asia, and we have lived in large urban centers in the US, as well. We are cautious of our surroundings, hold our belongings closely, and walk quickly and meaningfully in cities. When we arrived in Paris, we had to go through Gare du Nord to change trains, and I was well aware that this area could pose a potential for pickpockets, so we had our guard up.
All that being said, I believe there is probably nothing we could have done that would have prevented the style of pickpocket we encountered on the train. We were boarding the carriage when we were suddenly surrounded by five men. A few closed in around my husband, putting themselves between our children and him, and one grabbed my suitcase. I yelled, "NO!" and pulled it away, and as that was happening, one standing behind my husband had unzipped his pants pocket and was reaching in for my husband's wallet. My husband shoved him away and also yelled, "HEY!", and we think we caused enough commotion that the men didn't want to stick around, so they gave up on us and jumped off the train car before the doors closed. We were fortunate that they didn't get anything, but it certainly rattled our children as our first experience in Paris. It didn't end there, though.
After exiting the Metro line to walk to our apartment, we were followed by three men on the sidewalk (one carrying a roll-aboard suitcase), and saw two more walking toward us. They appeared to be trying to close in on us. We turned and stared at the ones behind us, and they stared back at us for a moment before dropping off into the street. When we started walking again, they again started following us. We waited a few moments at a cafe where there were people outside so as not to be alone, and eventually all five men wandered off. We hailed a taxi and got our luggage up to our apartment. We took a cab to the airport at the end of the trip and certainly wish we had chosen to do so at the beginning, as well.
I want to echo a thought that I've seen a couple of people say on here before: Please, do not take the RER and Metro with your luggage. Just spring for the 50 Euro taxi from CDG to your accommodation in the city. When you are traveling with literally all of your important documents and traveling possessions on your person, as you have to for airport arrivals and departures, you are simply too vulnerable to this ambush style of pickpocketing that appears to be happening on the Metro and close to its stations. It doesn't matter how savvy or alert you are--we were suddenly surrounded and outnumbered (twice!) and things could have gone a lot worse if we hadn't been lucky enough that these guys gave up on us quickly. If you are traveling with a backpack and that's it, maybe the train method works fine. But we were a family of two parents with two children and multiple suitcases, and there is simply no way to navigate the trains and stations without looking like a target whose hands are full of luggage and worried about keeping their children in line.
We enjoyed our trip, but this made for a difficult beginning.
Get a cab from the airport. It's worth it.