Sweet track is something that happened a very long long time ago. Way before there were cars or trains or anything like that, there were big animals called dinosaurs. And these dinosaurs used to walk around everywhere.
One day, it rained a lot - like a lot, a lot. So much water that it made a big puddle, just like when we play in the rain and jump in the puddles. But this puddle was much much bigger. It was so big that some of the dinosaurs got stuck in it.
As the puddle dried up, it created a sticky mud. And because some dinosaurs were stuck in the mud when it was still wet, their feet made imprints in the mud.
These imprints got hard as the mud dried up completely. And over time, these imprints or footprints stayed there because they were covered with dirt and rocks, and nobody could see them anymore.
Many years passed, and people started digging in that place. They found these imprints or footprints and were amazed to see them. They called them sweet tracks because these footprints were like a sweet story that the earth had kept hidden for millions of years.
So, sweet tracks are basically dinosaur footprints that got stuck in the mud and made a lasting impression on the earth's history.