Sforno on Numbers 1:4/ספורנו על במדבר א׳:ד׳

1איש ראש לבית אבותיו, this is emphasised to show that no one challenged the authority and authenticity of the people representing themselves as the “heads of his family.” When the count occurred, אתכם in the presence of the family heads each one testifying to the age of the individuals concerned, no one would dare to challenge the accuracy of the data provided by the family head.