DD2 has been a vegetarian since she was 14/15 and her daughter - my 6yo DGD - has never had meat nor fish. Both eat a very varied diet, lots of pasta dishes, soups, stews and stir fries. They are not averse to soya mince or veggie sausages or burgers which makes it easy to produce standard dishes e.g. spag bol for them. I used to make a meat and a meat free version of things like steak pie with a V or M in pastry on top but now I usually just make one big pie using veggie sausages, mushrooms and onions which everyone enjoys. Soya protein has less fat than meat and is also much cheaper. As they both have lots of eggs, beans, cereals, cheese, milk, yoghurt, etc. and their fruit and veg is mainly organically grown in their own garden, I do not think there is anything missing from their diet and they are both fit and healthy. Now that DGD is older she has been introduced to nuts which have become her snack of choice and she also has plain rather than milk chocolate for the iron it provides.
The only problem I have feeding DGD is the number of things which unexpectedly have gelatine as an ingredient - requires careful reading of packets.