We did Hong Kong in Febraury, with a 3.5 and a 2yo. We loved it. Disneyland was awesome, even DS, the 2yo could go on many of the rides, and he was so into meeting the characters. I would personally give Ocean Park a miss for little ones, great for older kids and adults though.
We stayed in Kowloon, and there is a huge park there, with playgrounds and a swimming complex. We started most days with a walk through there to help blow off some energy.
The streets are crazy packed, so the ergo was priceless and Disneyland had some jogger prams you could hire for cheap. We also took some reins/harness for the kids to wear if they wanted to walk.
The first day there we did a big red bus tour, which the kids were happy to sit and watch as we drove around, but that was coming off the back of a flight from the UK so they were pretty jet lagged.
The Peak is good,and the kids enjoyed the vernicular tram, but it was so foggy at the top.
There is a huge park on hong kong island as well, but we didn't get to that.
Be prepared for your LO to get a lot of attention, especially if they are blond. Both of mine are white blonde, and we had people wanting their photos with them, just touching their head as they walk by, and some just out right staring. It was cute to begin with but got a bit annoying by the end of the week, and DD was totally over it by then too.

HTH!