It means that the kid's mind or eyes is focused in his or her apple of his or her eye.The phrase apple of my eye refers to something or someone that one cherishes above all others. Originally meaning the central aperture of the eye. Figuratively it is something, or more usually someone, cherished above others. Origin:
"The apple of my eye" is exceedingly old and first appears in Old English in a work attributed to King Aelfred (the Great) of Wessex, AD 885, titled "Gregory's Pastoral Care".
Much later, Shakespeare used the phrase in "A Midsummer Night’s Dream", 1600:
"Flower of this purple dye,
Hit with Cupid’s archery,
Sink in apple of his eye"