Children under 15 can be included on their parents’ tourist cards, but complications occur if the children (by reason of illness, for example) cannot leave Mexico with both parents. Parents can avoid such red tape by getting a passport and a Mexican tourist card for each of their children.
Oaxaca travelers should hurdle all such possible delays far ahead of time in the cool calm of their local Mexican consulate rather than the hot, hurried atmosphere of a border or airport immigration station.