It’s the 35th birthday of the ubiquitous ‘Baby on Board’ decal. In 2000 the man who made it a thing, Michael Lerner, sold his kiddie gear company, and walked away with $38 million.

When the baby-on-board car decal made its debut in 1986, it was greeted as a fad. But 35 years later, it’s still as ubiquitous as the fear parents feel when strapping a new baby into a car for ...