Jim,
As insider responded, their policy is already rather generous. At least with a paid Bedroom, Amtrak is collecting the room fare, as well as a railfare for each person in the room including the child. With an award, Amtrak is getting nothing extra for that third person.
Yes I know that some will argue that Amtrak is also getting no additional revenue for putting 3 or 4 people in the family room. But that room was designed for 2 adults & 2 kids; the Bedroom was not. And one loses the perk of the ensuite bathroom in exchange for that extra capacity.
It may be a fine line, it may be an illogical line to some, but nonetheless that is where they chose to draw the line. I for one don't see them altering this rule.