How can I go to Ocean park from Chungking Mansions (New Guangzhou Hotel) via MTR?

you can take the tsim sha tsui mtr train to admiralty and then take a bus straight to ocean park from there

Well, take Tsuen Wan Line at Tsim Sha Tsui Station and get off at Central Station. Then take Tung Chung Line to Hong Kong Station, Exit E2. After that, walk to the central station and take public bus no.70 at Central (Exchange Square), and get to Aberdeen Tunnel Toll Plaza. Then walk to the north around 330 yards.

Or you can take public bus no.973 at New World Centre, Salisbury Road, and go to Wong Chuk Hang San Wai, Wong Chuk Hang Road. Then you will see the park directly. It takes 55 mins on the way. This way is an easier way for you and the child.