John Gill Commentary Numbers 1:22

"Of the children of Simeon, their generations, by their families, by their fathers` houses, those that were numbered thereof, according to the number of the names, by their polls, every male from twenty years old and upward, all that were able to go forth to war;" — Numbers 1:22 (ASV)

Of the children of Simeon, by their generations
(See Gill on Numbers 1:20).