Correct sentence: You can tell a jaguar from a leopard by its spots.
This sentence is grammatically correct. If you want a sentence that sounds a bit simpler for a 6-year-old, you can use:
- You can tell a jaguar and a leopard apart by their spots.
- Look at the spots to see if it is a jaguar or a leopard.
Short, simple explanation: Jaguars have big round groups of spots with a little dot in the middle. Leopards have smaller groups of spots and usually no dot inside. So you can tell them apart by looking at the spots.