be knee-high to a grasshopper

be knee-high to a grasshopper

  (humorous)
to be very young
Usage notes: A grasshopper is an extremely small insect.
The last time I came here I was knee-high to a grasshopper.
See also: grasshopper
References in periodicals archive ?
Little John may be knee-high to a grasshopper but he stands up for backbench MPs against Government ministers.