Personal Passive – Impersonal Passive – It is said

1. Personal Passive

When we put an object of an active sentence into passive, it becomes subject of the passive sentence.

Active sentence → The professor gave the students the books.
Passive sentence → The students were given the books.

We sometimes use a pronoun for the students or the books in its subject form (here: they).

Active sentence → The professor gave them the books.
Passive sentence → They were given the books.

We very often leave out the by-agent in the passive sentence (here: by the professor).

2. Impersonal Passive – It is said ...

The phrase It is said ... is an impersonal passive construction. This construction is used informally. It is said ... is used when one doesn't want to, or is unable to, site legitimate sources for what you are saying. It is, essentially, a way of claiming any position without justifying it.

Passive sentence 1 → It is said that children are afraid of ghosts.
Passive sentence 2 → Children are said to be afraid of ghosts.

The correct active sentence would be:

Active sentence → People say that children are afraid of ghosts.

Thanks to Steven.