in short pants

From an early 20th century practice of reserving short pants only for small children.

• "Near-synonym: in diapers"
• "Look, honey, this ain't my first rodeo, OK? I was doing this when you were in short pants."
• "Dr. Smith said a moment ago that we are scientifically adult but spiritually in short pants."

• in diapers
• in short trousers

• big-boy pants
• big-girl pants