I think not only is it reasonable but mandatory to apply some type/form of antiseptic to an “injury” of this nature.
Apparently a staff member in the office of CHIJ Toa Payoh Primary School, when asked for antiseptic, said it was not necessary and cleaned the knees with water and tissue.
If you were a responsible adult and a kid asked you for help in a situation like this, would you or would you not use antiseptic?