The advice came from the words of Luther Holt, who wrote “The Care and Feeding of Children” in 1894. He was celebrated for introducing “milk certification” in New York to ensure kids weren’t drinking a glassful of bacteria, and saved many lives. From his book:

Is not the excessive nervousness of many modern children due to the giving of meat, or at least aggravated by its use?

There is little ground for such a belief, unless an excessive amount of meat is given. Certainly cutting off meat from the diet of nervous children seldom produces any striking benefit.

What meats should be forbidden to young children?

Ham, bacon, sausage, pork, liver, kidney, game and all dried and salted meats, also cod, mackerel and halibut; all of these are best withheld until the child has passed the tenth year.

No bacon! You're only nine.