This episode is frequently cited in horror discussions for its claustrophobic "basement" scenes and the clinical, cold nature of the villains.
The couple is trying to "replace" their lost son. They keep the male babies that meet their specific criteria and discard the mothers and "imperfect" infants. Why It’s Notable [S5E5] Cradle to Grave
S5E5 - “Cradle to Grave” - Unsubs: A Criminal Minds Podcast This episode is frequently cited in horror discussions
The "interesting story" you're referring to is likely the episode " Cradle to Grave " (Season 5, Episode 5), which is widely considered one of the series' most disturbing and memorable "unsub" (unknown subject) cases. [S5E5] Cradle to Grave