How can an adopted child become a mahram without breastfeeding?

Mahramiyyah (being an unmarriageable kin) is established in three ways: lineage, suckling, and affinity (marriage). If there is no mahramiyyah by lineage or suckling between the sponsored child (makful) and his female guardian (kafilah), it can be established by affinity. For instance, if the sponsored child marries the daughter of the female guardian, the female guardian becomes a mahram to him, as Allah Almighty says: "and your wives' mothers." If this does not occur, the sponsored child remains a non-mahram (ajnabi) to the female guardian. We would like to emphasize that sponsoring orphans and foundlings is one of the greatest acts of worship.