You have a faulty premise. Most meat and dairy is healthy, if consumed in reasonable quantities. The exception is chargrilled red meat, which is correlated with colon cancer. There is evidence that vegan diets are dangerous for children. This study (https://academic.oup.com/ajcn/article/113/6/1565/6178918?log...), for example, found that vegan children were shorter and had lower bone density. Typical vegan diets lack the following essential nutrients either in part, or entirely:
* A
* B6
* B12
* D
* F
* K2
* CLA
* Carnitine
* Carnosine
* Cholesterol
* CoQ10
* Creatine
* Heme-iron
* Saturated fat
* Taurine
Of course a wise and studious vegan will carefully supplement all of these nutrients in the right balance on the right day. Most will not, and the risk compounds for children. An omnivorous diet is easy to get right, provided one doesn't over-eat.
* A
* B6
* B12
* D
* F
* K2
* CLA
* Carnitine
* Carnosine
* Cholesterol
* CoQ10
* Creatine
* Heme-iron
* Saturated fat
* Taurine
Of course a wise and studious vegan will carefully supplement all of these nutrients in the right balance on the right day. Most will not, and the risk compounds for children. An omnivorous diet is easy to get right, provided one doesn't over-eat.