Website
Also known as: Site
A website is a place on the internet where your lemonade stand lives, and it is open even when you are asleep.
A website is a place. Not a place you can walk to, but a place people can visit anyway.
Your lemonade stand on the sidewalk is open when you are sitting behind it. When you go inside for dinner, it is closed. A website does not go inside for dinner. It stays open all night, and it is open to people who live very far away.
Color this: draw your own place. Put your name on the sign. Now draw three people visiting it at three different times: morning, dinner time, and the middle of the night.
For the grown-up holding the crayon box:
A website is a set of pages served from a computer that stays on. The useful part for a child is not the technology, it is the change in availability: a physical shop trades your presence for sales, and a website does not. That is the same insight that later becomes the whole argument for owning digital property.