Police on Long Island are looking for the vandals who painted anti-Semitic graffiti in a park in Nassau County.

Children showed up for camp Thursday morning to signs of hate at Theodore Roosevelt Memorial Park in Oyster Bay.

Police arrived at the scene at 8:40 a.m., finding at least seven swastikas scrawled onto a picnic pavilion. Each swastika was about 10 inches in size and drawn using purple marker.

"At this camp we have ages 4 through 12," Oyster Bay Camp counselor Antonia said. "It's a big deal. It has to be taken seriously."

Authorities said it happened after midnight at Picnic Area 2, relatively close to the marina and the railroad museum. The town's public safety officers discovered the graffiti shortly after 7 a.m. Thursday morning.

Families who use the park are frustrated because they say it's the second time this summer they've seen troubling graffiti like the scrawls from MS-13.

"I want them to be able to bike ride at night time and in the morning, and not have to worry about this," Oyster Bay parent Vicki Walsh said.

Police are searching for the vandal or vandals responsible for the anti-Semitic images and investigating the crime as a bias incident. A $20,000 reward is being offered for information that leads to an indictment or arrest. Anyone with information regarding the crime is asked to contact the Nassau County Crime Stoppers at 1-800-244-TIPS. All callers will remain anonymous.