My daughter was five when she received a foam CD holder with plastic sleeves for all her music CDs. I explained to her that CDs are sensitive to light and heat, so she should not leave the holder in the sun.
During our home addition, the electrician was working in the backyard and she had gone to play in the sandbox, leaving her new CD holder on the patio table. My wife saw it and told her she was going to put it in the house.
My daughter stood up in the sandbox and said, "Mommy, make sure you put it where the sun doesn't shine!"