We live in a city and our children both know where their food comes from.
They help planting, feeding and picking fruit, peas, onions and potatoes. They also plant them after making a totally disgusting muddy hole. Last year's potatoes had the remains of a pair of toddler boxers entwined around a tuber!
We start with asking what meat do they want to eat? What animal does it come from? What is a baby one called? What is an adult called? Followed up with what noise does it make? So Lamb, sheep, lamb, Ewe or ram, Baaaa of varying pitch dependant on age and gender.
Although one was convinced for a time that potatoes grew in or behind dirty ears.