"L'uomo legge ai ragazzi."
Why would it not be "al ragazzi"? Haven't I seen that phrase before (or am I mixing up my Italian and French)?
"Al" is a compound of "a+il", so it's singular: "al ragazzo". For a plural you need ai (a+i) or agli (a+gli) depending on the following letters (ai ragazzi, agli squali)