How is that possible that each box still had three cupcakes ?

Question

There are three boxes of different sizes with three cupcakes inside each of the boxes in Sonia’s kitchen. In the middle of the night her son wakes up and goes to the kitchen. He opens a box and eat all the three cupcakes.

But in the morning Sonia finds out that each box still had three cupcakes. How is that possible ?

Answer 1

After eating the cupcakes her son puts the box inside the another, in such a way his mother finds every box filled with 3 cupcakes.