Tori Spelling and Dean McDermott's eldest child just turned 4 years old. On 'Lopez Tonight' (weeknights, 12AM ET on TBS), the couple shared that Liam already knows about the birds and the bees -- sort of.

Tori and Liam were watching a movie in which a guy and girl were just talking. Tori explained to her son, "He's flirting with her ... He likes her."

Liam responded, "Oh, he wants to have sex with her!" His stunned mother asked, "What is sex, Liam?" The preschooler intoned: "Mom, sex is when two adults get naked and kiss and move." George Lopez laughed and said, "That's right!"