The story
- Proto-Indo-European*(s)tew-
- Proto-Germanic*steupa-
- Proto-West Germanic*steupa-
- Old Englishstēop-
- Middle Englishstep-
- Englishstep-
- Englishgrand-
- Englishchild
- Englishgrandchild
- English todaystepgrandchild
From step- + grandchild.
Etymology from Wiktionary, CC BY-SA 4.0.