Dudley Dursley's children

The two children of Dudley Dursley and Mrs. Dursley were Muggles. They would occasionally be visited by their magical second cousins, the two sons and daughter of their father's cousin Harry Potter. While they played with James, Albus, and Lily, the children's fathers would sit silently together. Their fathers, Dudley and Harry, were on "Christmas Card" terms; which is to say, reasonably cordial, and in the habit of exchanging seasonal pleasantries such as Christmas cards, but weren't really quite friends. It is unknown if Dudley's children were male or female or if they were as fat or spoiled as Dudley was in his childhood.

Behind the scenes

 * Rowling once considered having Dudley show up at Platform 9 3/4 with a magical child in the epilogue of Harry Potter and the Deathly Hallows, but later changed her mind, stating that "any latent wizarding genes would never survive contact with Uncle Vernon’s DNA."
 * It is unknown whether Dudley's children know about magic. Harry Potter might have advised his children not to discuss magic around these Muggles and, if Dudley is anything like his father, he probably would never have mentioned the incidents where Harry used magic at 4 Privet Drive. Though, this can not be said for sure.

Appearances

 * J.K.Rowling Official Site

Notes and references
Дети Дадли Дурсля Dzieci Dudley'a Dursley'a