The former Arsenal captain is now academy manager at the club and went along with his Under-12s team to the tournament in Ypres, Belgium, this month.
Arsenal were one of six UK clubs who qualified for the tournament, along with six from Belgium, France and Mertesacker's Germany.
As well as the competition on the pitch the teams learnt about World War One on the fields where it was fought.
"It's very humbling and to be here and experience that for the kids is very powerful," Mertesacker said.
The teams visited war cemeteries, trenches and memorials. They also learnt about the Truce itself, when soldiers on both sides laid down their arms on Christmas Day, 1914, to exchange gifts and play football.
"By knowing our history we have full responsibility for what's going to happen next," Mertesacker said.
"Compatriots fought here. To remember Germans as well, for me, it's an honour.
"It means so much for us to be here and to be part of the Truce Tournament, in memory of the Christmas Truce, where soldiers came together and said, 'Let's get rid of that war for at least a day. Let's play some football, let's come together.'
"It gives you goose bumps when you are actually there. By being here and recreating the story and understanding what it was like, it will stick with them for their whole lives."
How his players performed on the pitch and off it was as educational for Mertesacker in his new job as the experience was for the boys.
"[I'm here] to get to know the players better for my perspective as academy manager, to get to know the emotions, what they go through," Mertesacker said.
"When they lose a game, everything is the worst moment in their lives. Just to give some perspective, reality, that's my job. I get a lot of personal development out of this as well.
"We experience a lot of teams from abroad and I think it's brilliant that the boys see and meet each other. They can even speak to each other, so mingling but competing against each other is a nice thing."