Ah-ha, been there done that! I took DS to HK in November to visit my Kiwi friend, he was 18 months at the time.
DO NOT GO TO CENTRAL. At least not unless you have DS in a backpack, the pavements have lots of steps on them, and it is hellish with a buggy.
Disneyland HK is quite small, but good fun, go midweek and it is very quiet (prepare to be photographed and stared at, the mainland Chinese go mad for little caucasian children, DS was a superstar ) - they have areas for little children, DS had a good time. There is also Ocean Park which is easy to get to, we saw giant sea lions etc and DS was enthralled by the pandas.
Go down to Stanley market for good shopping, loads of children's clothes cheap as chips, it's an easy cab ride.
No-one seems to use car seats, by the way, I sat in the back with DS on my lap (facing me) and under my seatbelt.
Oh, and take the Peak Tram up to the peak, fab views, and Star Ferry over to Kowloon!