Why do I say that?
The animal-product-free diet isn’t technically prohibited, and the ruling doesn’t necessarily equate veganism with child neglect. However, it will make it easier to prosecute parents who impose the strict diet and whose children have health problems.
and
However, opinions on this matter vary worldwide. The American Academy of Pediatrics, for example, is not opposed to vegan diets. "Although there have been case reports of children failing to thrive or developing cobalamin deficiency on vegan diets, these are rare exceptions," the academy notes on its website. "Multiple experts have concluded independently that vegan diets can be followed safely by infants and children without compromise of nutrition or growth and with some notable health benefits."
So if a kid in Belgium is visibly malnourished - ie, abused - and the mechanism of abuse is a restrictive diet that is not being applied correct, then the parents can go to jail. In general, the diet is not illegal in Belgium and one of the largest associations of childrens' doctors in the world (AAP) is not opposed to that restrictive diet (and comes close to endorsing it).
This is a non-story.