The reason I say that is because they are giving the animals a lot of growth hormones now, which is causing more and more children to have early onset puberty as well as weight issues. It also takes 10lbs of milk to make one 1lb of cheese. There is a reason, why those chickens look so big in Sainsburys. The farmers ensure that the chickens get big, we look for the biggest chicken in Sainsburys to buy = ensured revenue for the farmer. The impact this has on our health is of no importance to the farmer or Sainsburys, its about making money.
They aren't allowed to use growth hormones in the UK - you can avoid hormones and still eat meat if you simply buy British. The reason the chickens look so big in sainsburys is because some are injected with water! Again, this can be avoided by choosing carefully, or buying from local butchers which usually have full traceability.
I personally think that a vegan diet is very extreme for a small child. I can understand them being vegetarian in the main if meat is not the norm in the household, but every food has a
possible risk to it - I'd be far more concerned about the hormone/GM risks in soya than anything in UK cows milk.
I also share the opinion that has already mentioned about offering a wide variety of foods whilst they are small. I would worry about LO becoming a fussy eater, rebelling, or just having trouble fitting in when older because of it. As a meat-eating parent I would think twice about inviting a vegan child over for tea, as I wouldn't have a clue what to give them!