How to set a trigger on delete multiple parent and child rows? Below are the tables of relevance: 

Table_B
B_ID(PK)  Name  A_Id
1         A     1
2         B     1

Table_C
C_ID   B_Id(FK)
1      1
2      1


Now I want to delete rows from Table_B and from its child table Table_C.
Below is the query I am firing:

delete from Table_B where A_Id = 1


I want to delete all rows from its child too. Is it possible with a Trigger? I have made a Trigger on Table_B, but it deletes only one row; so I have to run a loop. 

Thanks.
I don't see the need to use a trigger. You could use two DELETEs:

DELETE C
FROM Table_C C
INNER JOIN Table_B B
    ON C.B_ID = B.B_ID
WHERE B.A_ID = 1;

DELETE FROM Table_B 
WHERE A_Id = 1;


If you want to use a trigger, you can use this code inside:

DELETE C
FROM Table_C C
INNER JOIN DELETED B
    ON C.B_ID = B.B_ID;


Justa as a note, remember that if you have a foreign key in that table, you could configure it ON DELETE CASCADE (but be careful with your deletes)