flight to hk shouldnt be a problem as my frenz brought her less than 1 year old to taiwan too. i guess you need to prepare thicker clothing for your son. disneyland i heard not very suitable for very young kid as they can play most ride. not sure about ocean park. but disneyland if dont intend to take much rides no harm bringing him in to walk and take photo and sit on those mild rides
rem to let him have water or food during take off and landing..