I have a five year old DD who has been vegetarian since birth. She also happens to have some sensory issues with food, which can make her challenging to feed. She eats more processed/soy-based food than I would prefer, but we have time to transition out of that as time goes on (just as you will be able to do with your children). For now, some favorites of DD's are:
baked
Quorn cutlets, marinated with various seasonings, just as you would chicken (These are a favorite for the whole family.)
fake chicken nuggets (Trader Joe's has the best ones, imo)
breakfast for dinner (scrambled eggs with veggie bacon and whole wheat toast or pancakes with fresh fruit and real maple syrup)
Many veggie kids and adults enjoy:
pasta dishes with veggie "meatballs"
Asian stir-fry with marinated tofu chunks
grilled cheese and hearty soups
bean burritos with grilled veggies
veggie dogs with chili and home-baked fries
loaded baked potatoes