Reagan Ingram, 9, paints a pumpkin on the Jock's Nitch Sporting Goods window Saturday at 837 Mass. About 50 painters participated in the 36th annual Halloween Paint-In.

Participating in her first Halloween Paint-In, 8-year-old Annie Olson stepped back to admire her canvas, the storefront of Sunflower Outdoor & Bike Shop. She beamed at her spooky masterpiece, which featured a black cat on a fence, a ghost and a rickety-looking haunted house.

Annie was one of more than 35 area children who picked up brushes and cups of paint for the 36th annual event, sponsored by Lawrence Parks and Recreation, Downtown Lawrence Inc. and the Lawrence Breakfast Optimist Club. They lined Massachusetts Street with parents in tow, decking out 30 downtown businesses in a frightful array of Halloween flair.

Local businesses donated their storefront windows for decoration, and Downtown Lawrence Inc. paid participants’ entry fees. Jim Rumsey, who helped organize volunteers for the event, said this allowed everyone who painted to receive a commemorative T-shirt.

Rumsey said the Paint-In began as a way to discourage vandalism during the Halloween season.

“Kids used to soak windows (of businesses) on Halloween. This is a way to make sure kids are doing something constructive,” said Rumsey, who said he has been involved in the Halloween Paint-In for 30 years.

Rumsey said though 35 children signed up to paint windows, as many as 50 total showed up to participate.

He said that numbers had lagged in recent years. But Duane Peterson, special events coordinator for the Parks Department, said the enthusiasm of local businesses helped to buck that trend and increase participation. He credited the Breakfast Optimist Club, Downtown Lawrence Inc. and Massachusetts Street merchant Jock’s Nitch for stoking interest in the venerable tradition.

Mark Olson, Annie’s father, said dwindling numbers did not discourage her.

“She’s wanted to do it ever since she was aware of it,” he said. “She’s got a sister who’s 6 who’s champing at the bit” to participate. She’ll have to be patient; the event was open to children in third grade or above.

As Annie scrutinized her Halloween still life, she said she was excited to display it.

“I just like the feeling that I am old enough to do something that everybody can see.”