Hi, I'm planning a trip to Hong Kong for 5 days in Jan 2nd week and staying in Novotel Century Hotel

Hi, firstly, I have to say that if you want your son to fully enjoy himself in Disneyland and Ocean Park for a whole day respectively, it is ok, because both of the attractions are the paradise for kids.

Your hotel is near Wan Chai MTR Station.
To Disneyland, you can walk about 5min from the hotel to Wan Chai Station, where you can take subway Island Line to Central. Then you can walk to HK Station to take Tung Chung Line to Sunny Bay, where you can easily catch the Disneyland Resort Line to the attraction directly.

To Ocean Park, you can take Island Line to Admiralty Station, where you can find bus no. 629. It can take you to the park directly.

As for your case, I suggest you spend 3-4 days in HK and 1 day in Macau travel. Here is a general itinerary recommendation:
1st day: You can visit Disneyland and Lantau Island (Ngong Ping 360) nearby.
2nd day: Ocean Park and the nearby Aberdeen.
3rd day: Go to Victoria Peak for a visit and then have a look at the Madame Tussauds. In the afternoon, you can go down the peak to Victoria Habor to enjoy the Symphony of Lights.
4th day: Take your son to Tsim Sha Tsui to wonder. The nearby Avenue of Stars and Star Ferry deserve visiting. In the afternoon, you can go to Central and Sky 360. If you have time left, the local snakes in Causeway Bay are worthwhile tasting.
5th day: Take a ferry to Macau to visit Ruins of St. Pauls, Largo do Senado, Venetian Resort and Fisherman Wharf as well as other surrounding attractions.