Lilly Foster-Lambert is a character on ABC/CBS family comedy Step by Step. She is portrayed by Jandi Swanson seasons 1-4 twins Lauren Meyering and Kristina Meyering as a young girl five years old during seasons 4–5 and as a ten-year-old Emily Mae Young during seasons 6–7 and 8.
Lilly is Frank and Carol's biological child, who is introduced in the season four episode "A Foster/Lambert Production". Originally depicted as a baby, Lilly's age is retconned to 5-years-old in the show's sixth season after the character is SORASed. For her age she is very smart and is always asking questions of everyone.