According to Shari Ireton with the Snohomish County Sheriff's Office, the young girl was waiting for a parent inside the store at roughly 3:30 p.m. last Monday when she was attacked.
The girl told police a man she didn't know walked up from behind and assaulted her.
The man, who is thought to be in his 40s, then left the store.
Police have released images from the store's surveillance camera in hopes of tracking down the attacker. The man stands 5'9" - 6-feet tall with a thin build and light brown or blond hair.
Anyone with information about the man is asked to call the police.