delete record with foreign key constraint to another table

Question

When I tried to delete row from datagridview refer to table Famille, I get this error is :

 An unhandled exception of type 'System.Data.SqlClient.SqlException' occurred in System.Data.dll Additional information: The DELETE statement conflicted with the REFERENCE constraint "FK_NatureCharge_Famille". The conflict occurred in database "Tresorerie", table "dbo.NatureCharge", column 'IdFam'. The statement has been terminated.

Table Famille

IdFam int
NomFam varchar(50)

Table NatureCharge

 IdNat int
NomNat varchar(50)

IdFam int

 

By the way, the Famille part can delete multiple row in datagridview. I tried to add delete the NaturCharge 1st (it begins with comment delete Nature)
The code in the rar file : 

 

an error shows with line (it is for Famille part) `cmd.ExecuteNonQuery();``

 Additional information: The DELETE statement conflicted with the REFERENCE constraint "FK_NatureCharge_Famille". The conflict occurred in database "Tresorerie", table "dbo.NatureCharge", column 'IdFam'.

 

It looks The DELETE statement doesn't seem to be correct

and the same error...