It took my son’s bar mitzvah for me to uncover just how many of my ancestors had been wiped out during the Holocaust.

For years, I’d assumed my late father’s grandparents and all of their siblings had escaped Eastern Europe before the atrocities. Already safe here in London, the only lasting effect of antisemitism on our family appeared to be our surname — anglicised from Seletsky to the less shtetl-sounding Sedley.

When we decided that Barney should celebrate his coming of age with something more meaningful than a family meal, we started to uncover a truth that perhaps I’d managed to ignore.

In the months up to the bar mitzvah, I’d read about Yad Vashem’s twinning project. Bnei mitzvah children are paired with a child who perished in the Shoah before they could celebrate their own, so they can honour their memory.

Perhaps it would be more personal if we could find a child connected to us? I vaguely recalled French relatives who’d died at the hands of the Nazis and emailed Brian Plen, one of my late father’s cousins and the self-appointed family archivist. I remembered a huge, well-researched family tree on his office wall.

He connected me with another cousin, Clarice Horelick, who lives in California and, although the same generation, slightly older, with more memories and actual correspondence from our Eastern European ancestors.

She shared that an entire branch of our family — my great-grandfather’s brothers and sisters — had stayed behind in the old country. All lost their lives, in ghettos or death camps. The story was stark.

Clarice suggested two of their first cousins (my second cousins) — Nanek Senitski or Numik Frankiel. The boys were my great-grandmother’s nephews — Nanek was her sister Tsirl’s son and Numik her brother Mendels’s boy.

Nanek died at Chelmno death camp and it is believed that Numik lost his life in Treblinka, having been sent there from the Warsaw Ghetto. Even now, inconceivable.

I contacted Yad Vashem UK to ask if Barney could be paired with one of them. After one of the very helpful ladies in their office had spent an hour searching with different spellings of their names and of the towns they lived in, we concluded that none of my family were on her database. There are four million names recorded but my family were absent.

There was no record of the atrocities they and their families suffered. Once our generation is gone, no one would remember them. We decided, as part of Barney’s bar mitzvah, to register the boys and their families so their memories will never be forgotten.

The process would take too long for Barney to be twinned with those family members so we were allocated another child. Boris Baruch Mauber, who had died in Belorussia.

We received a certificate with an account of how 10-year-old Boris had pretended to be dead after he and a group of Jews had been taken to a forest in Lyntupy to be shot.

He survived but a local man who this child had sought help from betrayed him and Boris was shot to death. Heartbreaking.

I did some research and discovered the record had been filed by his sister, Irene (pictured above with Boris) who survived the war.

Attempts to find her on the internet revealed a Facebook account that seemed to match her name, with the holder based in Seattle. I dropped her a line but heard nothing back.

A month later a response from Boris’s sister pinged into my Facebook messenger box. With uncanny timing, she had replied on Barney’s actual 13th birthday.

She told me she’d been touched by our attempts to reach her and sent me a link to a graphic account (on jewishgen.org detailing how she survived the war.

Reading it brought me to tears. She and her mother were the only survivors of a family of seven. What they went through is beyond comprehension.

Discovering our lost family and reading about Boris finally brought home the horror of those years. Even my computer game-playing son could comprehend the fear that poor Boris must have felt, playing dead in a pile of corpses which included his own family.

Barney may not have secured sponsorship to trek up a mountain nor cycled hundreds of miles for charity, but safeguarding the memories of his blood relatives proved just as worthwhile.

Our project ended up being a double mitzvah — for Boris and for a whole branch of our family, who will now not be forgotten.