Uma das abordagens pode parecer:
mkdir -p parent/child{1..10}
for d in parent/child{1..10}; do echo "This file is stored in ${d##*/}" > "$d/parent.txt"; done
Visualizando resultados:
$ head parent/child*/parent.txt
==> parent/child10/parent.txt <==
This file is stored in child10
==> parent/child1/parent.txt <==
This file is stored in child1
==> parent/child2/parent.txt <==
This file is stored in child2
==> parent/child3/parent.txt <==
This file is stored in child3
==> parent/child4/parent.txt <==
This file is stored in child4
==> parent/child5/parent.txt <==
This file is stored in child5
==> parent/child6/parent.txt <==
This file is stored in child6
==> parent/child7/parent.txt <==
This file is stored in child7
==> parent/child8/parent.txt <==
This file is stored in child8
==> parent/child9/parent.txt <==
This file is stored in child9