This is a subject very close to my heart as I am an amateur etymologist. Since I have been learning Chinese, I have also been collecting words whose sound and meaning are similar to other languages. I have quite a few.
Etymologists propose a language called Proto-Indo-European as the origin of the Indo-Germanic languages. One needs to look for words with similar sounds and meanings when comparing languages.
It is I think unreasonable to assume that the tribes that spoke this language only drifted westwards, none going east. However, as the West had only very limited access to China in the last 2000 years, they had neither the opportunity nor the desire nor the means or ability to include Chinese in their studies, which is their loss, as I see it.
Particularly 子, meaning son, child, seed may be related to German zeugen, which means, among other things, beget a child.
German uses -zeug as a suffix with a meaning like '-thing' in words like Spielzeug, Werkzeug， Bettzeug. Chinese has 子 in many combinations with a similar useage, such as 牌子， 量子， 脑子 .
May all just be coincidence, but the belief that the Proto-Indo-Europeans only walked westwards seems very egocentric of western scholars.