From the New Fowler's Modern English Usage:
The type many a prophecy though notionally plural (= many prophecies) always requires a singular verb.
In this case, are we talking about many a (boy and girl), many a couple? ... in which case the verb should be singular.
Or are we talking about many a boy and many a girl? ... in which case perhaps we follow xqby's and mtmjr's advice and the verb should be plural.