Don't get too wrapped up in the whole "It HAS to be before their birthday"
Someone in my family got an iPhone 4S for their birthday on September 9th. The iPhone 5 was announced September 12th. My entire family (even the non-tech savvy ones!) were strongly advising for them to wait just a few days, and if they still want a 4S, get it cheaper but still try and get the 5.. But nope. It HAD to happen on their birthday. Dumb mistake. Three days later, they realized they were dumb as well. It was a huge "I told you so" moment.
I think a better birthday present would be "We are getting you the newest tablet when it releases in a couple weeks!" Rather than getting a "brand new" tablet that suddenly becomes old just weeks later.
Even if the tablet is announced and released in time, you might not get it right when you are supposed to because of shipping delays when it first releases. So keep that in mind.