A better solution would be to do this in the database, assuming it's supported, rather than in code.
For example, with SQL Server, you can do this in a single command:
INSERT INTO Category_2 (ID, Label)
SELECT ID, Label
FROM Category
WHERE ID = @CategoryID;
INSERT INTO Product_2 (ID, Label, ID_Cat)
SELECT ID, Label, ID_Cat
FROM Product
WHERE ID_Cat = @CategoryID;