One look may be child's-play (1-3)
I believe the answer is:
'be child's-play' is the definition.
I can't tell whether this defines the answer.
'one look' is the wordplay.
'one' becomes 'I' (Roman numeral).
'look' becomes 'spy'.
'may' acts as a link.
Can you help me to learn more?
(Other definitions for i-spy that I've seen before include "Game played with young children", "Children's guessing game", "Children's alphabet game", "Child's game: ''. ... with my little eye'", "Wordgame".)