The claim is intended to sow the seeds of doubt by claiming that some vegan families had a child that died of malnutrition, and therefore veganism is dangerous or somehow at least unhealthy.
Uncommon events are given massive press coverage, particularly when they speak to narratives we construct in our heads, to generate clicks. In the realm of 1300 children died of neglect each year - this is even before Covid. How many of these stories are reported that are not trying to push some specific narrative?
The point is that those diets were as "vegan" as they were, say, "gluten-free" or "alfalfa free". Is your survival now contingent on eating alfalfa at every meal because a child on an alfalfa-free diet died of neglect?
This is just journalistic malfeasance. The list goes on and on for half-baked reporters searching desperately for justification for their own carnism, or trying to somehow cash in on some sort of anti-vegan sentiment. But this doesn't discredit veganism, any more than "A vegan drummer once couldn't keep tempo, therefore veganism interferes with your sense of time. Is it today right now? You won't know if you're vegan. Better go eat some McDonalds."
If you're so worried about starving children, consider that your choice to eat animal products is a leading cause of child death by malnutrition worldwide. People with money and control in these countries export grain fed to livestock to satisfy the Western demand. So your choice to "save the children" by concern-trolling vegan diets is actually counterproductive.
If you're reading this, you're not an infant. Therefore, you don't need to worry about the implications of veganism for infants if you aren't one, so this argument can't be used to justify eating steak or whatever. You can't possibly use that as a justification for killing animals for your own entertainment.