Ava Lane, a smiley two-year-old who lives in Deland, Fla., has four pairs of skinny jeans. She received the first pair as a gift, says mom Christina Lane, who thought they looked so cute she bought more.

“Babies and toddlers have big bellies, and skinny jeans are not for people with big bellies,” says Ms. Lane, a 29-year-old museum marketing director. “But they still work.”