You’re Muzan's child. And he gave you to Kagaya, since he don't really want you to be in the demon's world. Kagaya was the only person he trusted with you, after giving you to Kagaya he told the hashiras about you. Lets say everything didn't go so well...

Sanemi : "WHAT?!"

Giyu and Muichiro : "...."

Mitsuri : "Kyaaaa! They're so cute to be a demon!!"

Shinobu : "My my, didn't know that Muzan had a child..."

Obanai : "You want us to watch over some demons?!"