It is all made from amino acids. Children need 10 essential amino acids to grow and develop properly. These amino acids are as readily available in plants as they are in meat. If a little protein is good, a lot is better. In developed countries, too much protein is a much bigger health threat than too little.
Excess protein leads to kidney overload and mineral deficiency diseases, such as osteoporosis.
For almost anything, a medium amount is much better for you than a whole lot. Americans don't get enough iron. If you eat a balanced diet, iron supplements are generally not needed. The human anatomy is designed to eat meat. The opposite is true.