It was a fairly naive suggestion with some potential problems, but here's one way to unpack it using Eliezer's concept of Future Shock Levels (http://www.sl4.org/shocklevels.html) as a guide:

The parents are "old-style" humans.

For those with a shock level that is quite low, they would adopt the role of the parents. Although retaining perhaps disdain for new fads, etc., it's an understood social situation. This reframes what might be construed as unpleasant societal upheaval into a "standard" form of societal upheaval that occurs every generation.

For skeptical individuals who are at a sufficient shock level, the maturing children would be appropriate, redirecting the human vs nonhuman connotation into a cultural phenomenon where change and distinction over time are accepted or at least tolerated.

As mentioned in my comment above, although Lakoff is quite careful that his theoretical underpinning are solid (falsifiable, etc. etc.) the particular question of whether the family metaphor really is the dominant one in American political culture is not nearly as reliable.

If the transhumans are children growing up, who are the parents?

They have none. Transhumans are feral children growing up.