This is why I'm crazy

Different weekend, same story.
  1. 7:00 am Monday - Friday
    Kids are still sleeping and I often have to make many attempts to wake them up.
  2. 6:58 am Saturday
    Seven year old taps me on the shoulder to wake me up. It's almost 7 she says. "Well you can go downstairs and play or something. I'd like to stay in bed for just a little bit longer." 7 year old walks into her room (ignoring me completely as I realize what's happening and start saying her name over and over again)and wakes up three year old sister.
  3. Why does this phenomenon exist and how do I make it stop?