Hi Jen!
While I'm not aware of any children friendly movie houses in HK, we here in D.B. have been taking advantage of UA Citygate in Tung Chung. They often have kids friendly movies on before noon, and more often than not, you and your kid will be the only 2 in the house! My friend just took her 22-month-old in to see The Incredibles last week, and they were the only viewers. The boy lasted only for an hour, and they walked out, but that was a good start. Plus the morning shows are only$35 or less.
We haven't got a chance to try it out ourselves, but are so looking forward to it. Good luck with you little one(s).
Sara.