The meaning of a sigh

Going to be a busy afternoon. Picked all the kids up. Took them with me to get my eyebrows waxed (they love watching) and needed to get a quick healthy snack because I didnt make it to the grocery store, as I am driving and seeing only fastfood signs I must have let out a sigh. Lillie asks me whats wrong. Nothing. Lillie says but mom, that is your "I'm not going to say it...but you are making the wrong choice sigh". Wow. didn't know I sighed so often that my children have assigned statements to each of them.