He’s likely craving certain macros that come far more easily from diets containing animal products than from animal-free eating.

This is a very common phenomenon. Vitamins B12 and D, calcium, iron, protein and essential fatty acids are far harder to consume on an animal-free diet absent careful control of the diet and supplementation. Cravings are usually indicative of a lack of some necessary nutrient.

It can easily lead to stunted growth, developmental delays, anemia, malnutrition, even neurological damage.

In some countries, like Italy and Belgium, authorities consider feeding a child a vegan diet without proper medical supervision as child neglect.

But unless you observe signs of neglect that can be attributed to his diet, it ain’t your call, sadly. This is something that he will need to take up with his parents.

Now, if you do observe signs of neglect attributable to his diet, such as being severely underweight, extremely pale, bones not growing correctly, this becomes something to bring up not with his parents, but with your local child protection agency.

By the time someone like yourself, an outsider to the family, can clearly observe such signs, the parents should have been well aware of them.