Because the sounds of the words for son (tze) and paper (chih) have almost the same sound, so the boy is given an umbrella signifying the coming of age.
因「子」與「紙」同音，送給兒子表示成年；當做嫁妝則有「早生貴子」涵義，且「傘」中有四人，代表「多子多孫」。