During his first years, Casimir and his sister Agnes (born in 1137) lived with their mother Salomea in her widow land of Łęczyca.
Selama tahun-tahun pertamanya, Kazimierz dan saudarinya, Agnieszka (lahir tahun 1137) tinggal dengan ibunda mereka Salomea di tanah jandanya Łęczyca.