It is claimed two teenage boys had assaulted the victim near to an ice cream van at around 2.50pm on Sunday, 2 June.
Two 14 year-old boys have been arrested on suspicion of sexual assault and released on bail until Sunday, 30 June.
Anyone who saw or heard anything, or have any information, is asked to call Essex Police on 101 quoting the crime reference number 42/86555/19 or Crimestoppers anonymously on 0800 555 111.
Tags: Thurrock, Lakeside