I think he makes them, because there's always 4-5 and Jon has killed two and so did Meera
They are all connected to the one who turned them, thats why everyone but one dropped when Jon killed that one white walker.
Maybe they always send one from a different white walker on scouting parties for this exact reason, so he can let out an oh shyt call if the white walker gets dropped.
I think they just heard his call cause they were close enough.
I also wonder were the other white walkers made by the night king? or also by the children of the forest?