What is the meaning of [Little pitchers have long ears]

Sometimes ‘wide’ is used instead of ‘long’. A Little pitchers have long ears
is an earthenware jug with two ears instead of a handle. They are called
‘ears’ because they resemble human ears in the way they project from the
pitcher. ‘Little pitcher have long ears’ is another way of saying ‘Not is
front of the children.’ Although they may not give that impression young
children often take in every word spoken by their elders.

> ‘You know who I am, don’t you?’ the visitor asked Tommy.

> ‘Oh, yes,’ replied Tommy. ‘Dad says you’re the biggest idiot he’s ever met.’