What are the best source of proteins for vegetarian children? How much should be the daily intake for different age levels?

On top of what has been mentioned by Nooraini, you can try Quorn if your child is above a year old. Quorn is a vegetarian source of protein. Quorn is a mycoprotein, which means it’s made from fungi, such as mushrooms and not soya based like textured vegetable protein. I've personally tried quorn and it tastes really good. My vegetarian friends in Sweden do feed their kids Quorn products on top of other sources of proteins like quinoa, corn, spinach, tofu and nuts. However, do note that some people have reported allergic reactions to mycoprotein, but this is rare.