Here's the reason for 1997 from the official Hong Kong Disneyland website:
Complimentary Deluxe Annual Pass Offer
To celebrate the 10th anniversary of the Hong Kong Special Administrative Region (HKSAR), Hong Kong Disneyland invites every child born in 1997 to enjoy a whole year of complimentary visits to the Park!
How it works
Every child born in 1997 can get a complimentary Deluxe Annual Pass between 15 May and 1 July 2007 to enjoy the magical delights of Hong Kong Disneyland.
In other words, it's been ten years since Great Britain turned Hong Kong over to China.
This reminded me when Barnum and Bailey Circus put out something similar (but certainly not as expensive) for all children born in 1993.
They gave them all free passes to see the circus any time it was in their area.
The certificate was so lovely we actually framed it and never used it!
There are sure to be some very lucky and very happy parents out there!