When my nephew was in elementary in the 80s, his mother would send him to school with a mustard and lettuce sandwich. No meat. Not variations. Just two slices of white bread with a slather of mustard and a leaf of lettuce.
Why?
Because that was all he would eat. He wouldn’t eat ‘school’ meals. All he wanted was those mustard and lettuce sandwiches.
Even at home, that was about all he would eat. By junior high, he had discovered a liking for hamburgers, though.
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My sister did talk to the teachers early in each school year and explain the spartan lunch she sent with him.
At scout camp good, though rather plain meals are served.
There is also a table with peanut butter, bread, and jelly. Some kids always eat the pbj because that is all they eat
Kids have weird appetites. My 18 year old nephew hasn’t eaten since he was weaned. He looks and acts as healthy as an ox.