how to delete item in Cascaded manner

I have an application in that i am using SQLite DB to cache the files and folders. SQL query for creating tabel looks as bellow.

CREATE TABLE b 
(
Id INTEGER  PRIMARY KEY,
ParentId INTEGER  NOT NULL,
FileName VARCHAR(260)  NOT NULL,
FOREIGN KEY(ParentId) REFERENCES id ON DELETE CASCADE
);

Folder structure looks like

Folder1
    Folder11
        file1
        file2
        file3
        file4
    Folder12
        file121
        file122
    Folder13
Folder2
    Folder21
    Folder22
Folder3
    Folder31
    Folder32
    Folder33
    Folder34

My requirement is:

If i delete a folder then all the childs of that folders needs to be deleted.

for that i written a query

DELETE FROM a WHERE ParentId=x;

But is not working. Is there any mistake in sql query.