In the long run it may be worth getting a towbar fitted and using a bike rack that works using that.
Your kids and their bikes are only going to get bigger aren't they!?!
You can pick a second hand one up fairly cheap:
http://cgi.ebay.co.uk/VW-bay-window-camper-type-2-Witter-tow-bar-towbar-/110540665092?cmd=ViewItem&pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item19bcbcb104#ht_500wt_947
________________________________________________________________________________
Max SportsKombi - The Bay Racer and Tango - the Fizzy Kombi
@brazilianvwbay