Yes, it is possible to go and back in the same day. For you are staying in Taipa, you can take ferry to Taipa Temporary Ferry Terminal. Cotai Jet provide ferry to HK every half a hour. Choose to alight at HK-Macau Ferry Terminal in Shueng Wan. Then take MTR for just one stop to Central. Get out from the exit to Central Star Ferry. Therer is bus 926 running to Ocean Park. Bus timetable: 09:35, 09:55, 10:15, 10:35, 10:55 all in the morning. The same way back to Macau. Ferry back to Macau is even available after midnight, so don't worry about the time.

Thanks Jason for your reply. How long would it take from central to ocean park? I read other post mentioned about Admiralty station, is it same with the Central that you mentioned?

Is it advisable to visit Stanley market at night (mean after the ocean park)? How far is it from Ocean park (journey time)? What bus/MTR to take to back from Stanley market to Ferry terminal (back to macau), when is the last bus?

Hi, Ms Teo, it is the same bus. The bus is just available in the morning in Central, if you coming in the morning, it suit for you to take for central is closer to the ferry temrinal. No problem to take it in Admiralty. It takes some 20 minutes from Admiralty to Ocean Park, so, half a hour or so from Central. Possible to go to Stanley market after Ocean Park, but the store and bazaar seems to be closed at 7pm. Walk about 10-15 minutes from the main entrance of the Oean Park to the bus stop of HK countryside Club. There are bus routes to Stanley market. Stanley Marcket area has direct bus back to Central Exchange Square, such as bus 6, 260. Last bus at 00:00. If you haven't been to Victoria Peak, this is a nice choice after Ocean Park. You can get around the harbor area for the light show or see the Avenue of Stars? Just my opinion. Have fun!

Ms. Teo.
I don't think you can arrange travelling between Ocean Park and Macau within a day in available....except, you are intend just look around the Park door and that leave there, or else, I advise you just go to Macau only, because yr's 2 kids can't be a fulled to enjoy there fun....there are big and many many show, animal, cences waiting you come there.