first thing u need to get letter from ur company showing how much is ur salary, which position u r working and they dont have problem that u will sponsor ur son.
second thing u need to get statement from back for ur account for 6 months.
third get salary certificate showing how much ur company is transfering ur salary to the bank.
fouth get ur labour contract copy and plus ur offer letter copy also.
fifth get the copy for electric and water bill (for the place u r staying).
then get the form from labour office to apply family visa and ask some typist to type that form and then attached all those documents with that form and submit to labour office and hopefully u will get reply within 5 to 6 working days.
all those documents are important.