Zackary Drucker, a producer on “Transparent,” said she did not think that these two performances would necessarily begin an immediate trend of transgender children appearing in droves on TV. For one reason, the talent pool is drawing from a relatively small population. The number of transgender children in the United States is unknown, and little research has been done on early childhood gender identity. But some estimates suggest that the number of transgender adolescents amount to under 1 percent of that population.

Still, Ms. Drucker, who is transgender, remains optimistic that young people will continue to expand a growing transgender presence in pop culture.

“Mainstream culture is catching up,” she said. “At its best, that’s what entertainment can do: present a world that glimpses into the future.”

The “Transparent” crew is looking ahead by hiring transgender writers, producers and actors, even as the show is led by Jeffrey Tambor. During his Emmy acceptance speech for his portrayal of Maura, Mr. Tambor said he would not be unhappy if he were the last cisgender man to play a transgender woman on TV. (A cisgender person is someone whose gender identity reflects the sex he or she is assigned at birth.)

Introducing young talent to large audiences may be a way forward. Sophia and Jackson’s performances are used as different storytelling devices, and one portrayal is glossier than the other: On “Modern Family,” Jackson’s character, Tom, shows that a happy, well-adjusted transgender child interacts with the world in a way that is indistinguishable from cisgender children, while at the same time exposing any preconceived notions held by the adults in the room.