If the wife is only riding with the children, no reason to change anything at all. I'm guessing the children's bikes don't have much gearing. Just use 1 ring and all of the gears. If she's going to be doing tougher rides, then you can change something. My wife would rather piddle around on her vintage mixte with 2 x 5/stem shifters than her souped up road bike with 9 speed rear/brifters.