How do you know when your kid is tired?

How about when you are talking to them while you are cooking and literally mid-sentence they pass out on you? While at the table mind you. LOL Poor thing. This was two nights ago. We made dinner a little late because Miguel got home late and she just passed out. Of course this may be one of the reasons she was tired.
We spent a good portion of the early evening running around outside pretending to be a butterfly fairy. She was "flying" up and down the driveway and around the yard. Cute. Unfortunately for me she has taken to wanting to wear the wings, the fairy crown, and carry the wand EVERYWHERE we go. Le sigh.......2 year old girls. Gotta love them. I will remember this fondly when I am older. Right now.......well let's just leave it at that.