Cut tofu crosswise into 8 (1/2-inch-thick) slices. Arrange tofu on several layers of paper towels. Top with several more layers of paper towels; top with a cast-iron skillet or other heavy pan. Let stand 30 minutes. Remove tofu from paper towels. Cut tofu into 1/2-inch cubes, and toss with cornstarch.
Prepare noodles according to package directions, omitting salt and fat. Drain well; set aside.
Combine ketchup and next 3 ingredients. Heat 1 tablespoon oil in a nonstick skillet over medium-high heat. Add tofu to pan; sauté 7 minutes or until golden. Remove tofu from pan.
Heat 1 teaspoon oil in pan. Add eggs and egg white; cook 30 seconds, stirring constantly. Remove from pan. Heat remaining 2 teaspoons oil in pan. Add noodles; cook 3 minutes. Stir in ketchup mixture; cook 30 seconds. Add egg mixture; cook 1 minute, stirring often. Remove from heat; stir in onions and cilantro. Top noodles with tofu; sprinkle with peanuts and serve with lime wedges.
for your toddler: Omit the Sriracha and green onions; adults can add them to their servings later, if desired. Serve a spoonful of noodles tossed with the sauce and 3 to 5 tofu cubes in a small bowl. Cut the noodles into bite-sized pieces.