تعريف ومعنى "[catch] {sb} with {one's} [hand] in the cookie jar"

What is the origin of the idiom "catch someone with their hand in the cookie jar" and when to use it?

The idiom "catch someone with their hand in the cookie jar" is originated from the act of sneaking cookies or sweets from a jar without permission. This expression is often used when someone is caught red-handed engaging in an activity they shouldn't be.