Michael's rowing was first up, followed by Simon's game.
"We popped a bottle of bubbly after Michael and then had to re-cork it for Simon," joked Mrs Arms.
They are modest about their contribution to their sons' success.
"They have always had the talent. We just laid the foundation and supported them. This is really their moment."
Sporting talent is in the family's blood - the boys' great-great-uncle, Harry Kerr, was the first New Zealander to win an Olympic medal, in 1908.
Mr Arms said they encouraged sport in the family, but were open to whatever the boys wanted to try.
"It was always their enjoyment of the sports that drove them and made them successful.
"We have just enjoyed the ride."
Both boys attended Auckland Grammar, something their parents said was an important factor in their success, along with coaches.
"Some parents try to get involved with coaching, but we have always taken a step back and really trusted the coaches to do their work."
Simon's team lost their game but Mr Arms said the end result wasn't what was important - he was just proud his son had reached international level.
"You always have to give it a go but in sports you have to be prepared that there is always a loser."
The Under-20 All Whites' next game is later this week and the Arms said they were expecting another late night.
Michael Arms, 23
* Won the gold medal in the double sculls with Robbie Manson at the World Rowing Cup regatta in London.
* Tried various sports before rowing in high school.
* Studies sport science through Massey University.
Simon Arms, 20
* Defender for the New Zealand Junior All Whites who played in the Under-20 world cup opener in Turkey against Uzbekistan.
* Played soccer since he was 4.
* Studies architecture at the University of Auckland.