If you immediately take MTR to Admiralty and take Bus629 to Ocean Park, it would be around half past one in the afternoon. If you get out of the park at around 06:40 P.M and take Bus 629 back to Admiralty and then take MTR Tswan Wan Line to Tsim Sha Tsui Station Exit F and walk to Avenue of Stars, I think you'll catch the show.

If you choose the other option, take the kids to the Peak, you can take them take the Peak Tram and visit Madame Tussauds Wax Museum, surely the peak is not as exiting as Ocean Park, but kids will also have a good time there.