My older child (already a student) brought a car for the younger brother (4 years old). He hid behind his back, stood in front of him and asked as appropriate:
In which hand is the gift?
On the right!
The elderly pulls his empty hand forward.
On the left!
The oldest behind the back moves the machine, showing the empty left hand.
A second pause, then the younger, enthusiastically solving the logical problem of the man, shouts out:
In the pop then!!...