Inuyashas childhood is very difficult and he is alone and without friends that’s why toga give the sword to inuyasha to protect and guide him,, while setsuna is protected by miruko and seal his demon side,, miruko always seal setsuna’s demon side when setsuna is on berserk, while inuyash is always alone when he was a child, inuyasha has no friend on his childhood that’s why giving the sword to protect him is very wise decision. Jaken protect setsuna and intrusted to half demon bat while towa is on safe era.
For someone who let his daughters to be on their own so they could learn to survive, Sesshomaru really is protective... I mean, he watched over them secretly and showed up to save them whenever they're really in true danger. And, it's amazing how much faith he had on his daughters. He believed all along they will grow up strong and reliable.