Two of our favorites are shepherd's pie and tacos. Both my one year old and four year old love them.
For shepherd's pie I sautee sliced fresh mushrooms, diced red bell pepper and zucchini. I'll stir in a can of cream of mushroom soup, a package of meatless crumbles and enough frozen veggies to make the mix thick and cassaroley (sorry, I never measure this one). I also add in some sage, rosemary and garlic. Once everything is hot spoon into a casserole dish and top with either sliced or mashed potatoes and shredded cheddar. Bake uncovered on 350 until the cheese is melted and bubbly. The variations on this recipe are endless depending on what veggies you have on hand and the seasonings you decide to use. I also replace the crumbles with black beans.
We also make tacos using taco seasoning and crumbles instead of ground beef. Serve with a can of black beans (I cook the beans diced red bell, diced onion, frozen corn, cumin, garlic and a bit of lime juice), shredded lettuce, sour cream, brown rice, diced tomatoes and shredded cheese.
There are several vegetarian cookbooks geared to families with kids. I've been told that the one by Nava Atlas is really good. Deceptively Delicious is mostly a meat-eater's cookbook, but if you have a friend with a copy check out the tofu nuggets and the mac & cheese. Both go over well with my little ones. Good luck and happy eating!!