Rashi on Numbers 1:2/רש"י על במדבר א׳:ב׳

1למשפחתם — [TAKE YE THE SUM OF THE CONGREGATION …] AFTER THEIR FAMILIES — in order to ascertain the number of individuals in each tribe.

2לבית אבתם BY THE HOUSE OF THEIR FATHERS — One whose father belongs to one tribe and his mother to another tribe shall take his stand with the tribe of his father (cf. Bava Batra 109b).

3לגלגלתם BY THEIR POLLS — i. e. by means of shekels — “a beka a head (לגלגלת)”, as was prescribed on a previous occasion (Exodus 38:26).