I don't work for BA, but another UK based airline. One of the points on the BA website states;

Passengers who are travelling with anyone who would require their assistance in the event of an emergency.

At our airline, if we became aware for example that we had parents sat in an exit row and the children in the row behind, we would move the parents out of the exit row. We want the people in the exit row in an evacuation to be focused solely on opening the exit and starting the evacuation, not trying to gather their children.