The boy replied: "Ma'a Nonu.''
Mr Key said: "Oh, he played well on Saturday. But they were a bit sad 'cos the Hurricanes lost.''
Mr Key later chatted with Mr Malielegaoi and some other delegates while sipping on coconuts.
The Kiwi Prime Minister proudly held up his coconut drink and said to media: "You can't get fresher than this!''
The playground's reveal follows an initiative launched by the Samoan Government last year, dubbed: The Apia Waterfront Development Project. The idea is to develop the area, which includes a seawall that runs from one side of Apia to the next.
New Zealand also has a role in the project; offering financial and technical support from Kiwi coastal scientists.
Mr Malielegaoi told the public that the idea for the waterfront development project was inspired by Auckland's waterfront, which he said was a bustling place for people to enjoy.