Preheat oven to 300 degrees. Stack the tortillas on top of each other. Wrap in aluminum foil and place in the oven to warm while you prepare the chicken.
Whisk together sour cream and salsa in a small bowl season with salt and pepper. Cover and refrigerate.
Heat the grill pan or nonstick pan over high heat. Brush the chicken on both sides with oil and season with salt and pepper. Cook the chicken until golden brown on both sides, about 4 minutes per side. Remove to a plate; drizzle with the lime or lemon juice. Let rest for 5 minutes. Using a fork, flake the chicken into large pieces.
Set up a taco bar for your kids. Place remaining ingredients in small bowls. Wrap the warm tortillas in a clean dishcloth on a plate.
To serve, put some chicken in the center of each tortilla. Top with onion, tomatoes, and cabbage or lettuce, then drizzle with sour-cream sauce and cilantro leaves if desired.