Who was the third kid with Harry's and Ginny's kids?

Question

I just watched The Deathly Hallows Part 2 on TV (so apologies for no screen shot). At the end when we see Harry's and Ginny's family enter the station to board the Hogwarts Express there are 3 kids

• One is their son who Harry talks to about the Sorting Hat's decision (as he expressed concern about being put in Slytherin)

• One I assume is their daughter who is too young to go to Hogwarts

There was also a third kid who went into the station just before Harry and his son entered together, the one with dark curly hair. He is also seen on the train with Harry's son when the kids wave to their parents as the train leaves.

Who is this third kid?

Answer 1

This is James Potter, Harry and Ginny's oldest son. In the book version of Deathly Hallows, the three children have the following exchange, which more-or-less matches with the dialogue you describe:

"It won't be long, and you'll be going too," Harry told her.

"Two years," sniffed Lily. "I want to go now!"

The commuters stared curiously at the owls as the family wove its way toward the barrier between platforms nine and ten, Albus's voice drifted back to Harry over the surrounding clamor; his sons had resumed the argument they had started in the car.

"I won't! I won't be a Slytherin!"

"James, give it a rest!" said Ginny.

"I only said he might be," said James, grinning at his younger brother. "There's nothing wrong with that. He might be in Slytherin"

^{_{Harry Potter and the Deathly Hallows Epilogue "19 Years Later"}}

Although I haven't seen the movie version, the picture of James Potter on the Harry Potter Wikia seems to match your description:

The first child you describe is Albus Severus Potter¹, Harry and Ginny's middle child, who is starting his first year at Hogwarts:

The second child you describe is Lily Potter, Harry and Ginny's youngest:

And here's a picture of the kids waving from the Hogwarts Express²:

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¹ That poor, poor child

² As to the identities of the girls in that picture, the one nearest the window is Rose Weasley, Hermione and Ron's oldest child. The other two are unidentified as far as I can tell, but one of them is possibly Bill and Fleur's daughter Victoire Weasley. However, no actress was credited for the role, so we can't be sure. I've posted a follow-up question, so please weigh in if you have any more info