When the boy was born, like all Spartans, he was inspected. If he'd been small or puny or sickly or misshapen, he would have been discarded.
16 seconds sound clip from the 300 movie soundboard.
You can hear this line at 00:01:08 in the Blu-ray version of the movie.
Quote context
[...]
- From the time he could stand, he was baptized in the fire of combat.
- Taught never to retreat, never to surrender.
[...]