I have not found information relating directly to this individual child you ask about, but there is other discussion of imprisoned children coping with the horrors around them through play.
A blog site article Kids, the Holocaust, and “Inappropriate” Play discusses this topic, and brings up a couple of references you might find enlightening,
The Eisen book is not 'visible' though Amazon or Google books (for me at least), but the blog does give us some quotes from page 169 of the Grays' book describing other, very similar circumstances to those you describe:
But the children would have none of that. They played games designed
to confront, not avoid, the horrors. They played games of war, of
“blowing up bunkers,” of “slaughtering,” of “seizing the clothes of
the dead,” and games of resistance. At Vilna, Jewish children played
“Jews and Gestapomen,” in which the Jews would overpower their
tormenters and beat them with their own rifles (sticks).
Even in the extermination camps, the children who were still healthy
enough to move around played. In one camp they played a game called
“tickling the corpse.” At Auschwitz-Birkenau they dared one another to
touch the electric fence. They played “gas chamber,” a game in which
they threw rocks into a pit and screamed the sounds of people dying.
One game of their own devising was modeled after the camp’s daily roll
call and was called klepsi-klepsi, a common term for stealing. One
playmate was blindfolded; then one of the others would step forward
and hit him hard on the face; and then, with blindfold removed, the
one who had been hit had to guess, from facial expressions or other
evidence, who had hit him. To survive at Auschwitz, one had to be an
expert at bluffing — for example, about stealing bread or about
knowing of someone’s escape or resistance plans. Klepsi-klepsi may
have been practice for that skill.
Note that none of these tragic stories list any individuals by name. If this individual discussed by your tour guide survived to relate the specific event you are seeking, I did not uncover it yet. This does, however, shed some light on part of your question which states
how this kind of event can alter children's minds