I'm sure it's partly because of those very rare cases in which a vegan child ends up malnourished. In view of the fact that across Europe large sections of the population are considered as suffering from malnutrition, these cases are probably newsworthy because they are so rare, but they distort the picture, which may be the intention in some cases.
The level of ignorance about veganism in some quarters is still astonishing:
https://www.theguardian.com/lifeandstyle/2016/aug/10/parents-children-vegan-diet-prosecuted-italian-law
I'm sure it's partly because of those very rare cases in which a vegan child ends up malnourished. In view of the fact that across Europe large sections of the population are considered as suffering from malnutrition, these cases are probably newsworthy because they are so rare, but they distort the picture, which may be the intention in some cases.