What is the infinitive phrase for children were asked to play quietly?

The infinitive phrase in the sentence "Children were asked to play quietly" is "to play quietly".

Here's why:

* Infinitive: The word "to" followed by a verb (play) forms the infinitive.

* Phrase: A group of words that act as a single part of speech. In this case, the phrase acts as an adverb modifying the verb "were asked".

The infinitive phrase tells us *what* the children were asked to do.