I wouldn't try to reproduce that layout, it gets ugly in narrow screens. I'd rather go for something like:
First child
"I am Jack."
Second child
"And I am Jill."
Code:
<p><span class="speaker">First child</span>"I am Jack."</p>
<p><span class="speaker">Second child</span>"And I am Jill."</p>
Code:
p { margin: 1em 0; }
span.speaker {
display: block;
text-align: left;
font-size: 80%,
font-style: italic;
}