Before anything else: God loves you all the time, and He's happy when you tell the truth. He doesn't get mad at whoever comes close to tell Him, He helps.
Have you ever played with soap bubbles? They're beautiful, right? They turn colorful in the sun, float up in the air, and everyone looks at them.
But notice something: how long does a soap bubble last? Just a few seconds. It pops on its own, without anyone touching it. It's pretty and it doesn't last.
A lie is like that. At the moment, it even seems to solve the problem. You tell it and no one finds out, and it looks like it worked. Except the lie pops on its own, the same way the bubble does. One day someone asks a question, another day someone remembers something else, and that's it.
And there's a tiring thing about lying that almost no one tells kids. After you tell one, you have to keep remembering it. You have to be careful not to tell it differently next time. It's too much work.
The truth is the opposite. It's like a little stone, not as shiny as the bubble, but it doesn't pop. And the best part: you don't need to remember anything, because the truth is just what really happened.
And here's something important: if you already told a lie, tell the truth soon. A small bubble pops easily and doesn't splash anyone. The more time passes, the more people end up getting splashed too.