We have two 360 software updates on our v6 boxes but have to use same pin for both boxes ?

[Bettyrose]

We have two v6 boxes one upstairs one down stairs with two different pin numbers my box my sons box we have recently done a 360 software update on both boxes we carnt have two different pins it will only let us have the same pin for both boxes why his this 

[jb66]

The pins are for parental control, not sure what benefit of having different pins