Girl and boy crossing top of Italian lake (7)
I believe the answer is:
galilee
'lake' is the definition.
(the Sea of Galilee is a lake)
'girl and boy crossing top of italian' is the wordplay.
'girl' becomes 'g'.
'and' says to put letters next to each other.
'boy' becomes 'Lee' (boy's name).
'crossing' is an insertion indicator.
'top of italian' becomes 'ali' (I can't explain this - if you can you should give a lot more credence to this answer).
'g'+'lee'='glee'
'glee' enclosing 'ali' is 'GALILEE'.
(Other definitions for galilee that I've seen before include "District where Jesus preached" , "Holy Land sea" , "Holy land region" , "Biblical Sea west of the Jordan" , "Famous sea in Bible" .)