I have booked the appointment at Croydon for 28th Aug 2012 for Me (Main applicant), Wife and my 4 yr old son. I have all my documents in place and hopefully my application should sail through smoothly

Our current BRP card has the valid till date of 24/09/2012.
My question is,
Can my wife and son travel on this card and the ILR approval letter (If it is approved) as the current BRP card will be valid when they travel or do they have to wait till the new card arrives?
Many Thanks
Wasim