This happened to me several years ago and I do not recall all of the specifics however it went something like this:
I was umpiring a Little League tournament game and during pre-game i noticed a couple of kids in the stands of the traveling team dressed with the same exact pants as the team on the field. The team only had 10 kids on the field in full uniform for introductions and in the dugout. With that sense of fairness instilled in me I had a strong feeling that these kids were actually "alternates" possibly on the affidavit ready to suddenly appear should the need arise.
As it was, I did not take any action, nor did the opposing team mention it. For all I know they could have been younger brothers from another team. But I always think back about this and it bugs me that maybe I should have asked their names to see if they were on the affidavit or it should not be an area of my concern.
Our umpire often dual role as TD's so we do have that authority,