The presentation of the relationship Buddha-humanity in terms of father and son also deserves attention. The term “the Buddha’s children” appears often in the sutra to indicate the Buddha’s disciples, bodhisattvas, and all those who practice according to the teaching of the Buddha. They are called “children born of the Buddha’s mouth.” Nichiren underlines that only a Buddha coming from this Sahā world can be considered father of the beings living in this world. Other Buddhas who abide in different parts of the universe are not qualified because they do not have this bond, thus their existence is almost irrelevant for people, or at best an upāya.
A Buddhist Kaleidoscope; Lucia Dolce, Between Duration and Eternity: Hermeneutics of the ‘Ancient Buddha’ of the Lotus Sutra in Chih-i and Nichiren, Page 233-234