Growing up in the 60's and 70's it was very common for a parent to say to a child, "Do NOT take more than your stomach will hold!" OR "There are starving kids in China!" (some parents said, "Africa"-- my parents preferred China for some reason.

Photograph with caption "Cafeteria Lines in Mess Hall

 at Naval Barracks Area," U.S. Naval Ammunition 

Depot, Hastings, Nebraska., 1944?

Taking a closer look we can see that the sign on the wall 

says

that 'any wasting of food will be followed with disciplinary 

action'. (can that advice even be comprehended by kids 

these days?)