In a mixing bowl combine the olive oil, mustard, lemon juice and garlic. Blend until smooth and season to taste with salt and pepper. Cut the kids portion of chicken breasts into 1-inch cubes; leave the adults' portion whole. Marinate all of chicken in the mustard mix for as long as possible. Season bread crumbs with salt and pepper. Dip the chicken in bread crumbs so all sides are well coated. Heat the butter and vegetable oil in a large skillet and saute for 5 minutes a side or until just cooked through. Variations: if kids don't like mustard mix, marinate their portion of chicken cubes in ketchup, a barbecue sauce or some dressing they love, then dip in bread crumbs and proceed with recipe.