This was everyone in antiquity, not just the Gauls. There's a ton of archeological evidence from Roman forts and camps of their wives and families following them, along with the fact that the #1 way for a Roman general to say "I'm being a hardass disciplinarian" was to kick as many noncombatants out of the camp as possible.

The "camp follower" was mostly done away with in the ancient before-time of the 1800s, when railroad logistics and better communications allowed the State to centralize their organization to the point where they could finally get rid of all of the women doing laundry / cooking meals / maintaining equipment while doing some hookin' and sutlering on the side.