Colin Creevey... and his brother Dennis.
In the Chamber of Secrets Colin unabashedly shares his Muggle-bornness:
It’s amazing here, isn’t it? I never knew all the odd stuff I could do was magic till I got the letter from Hogwarts. My dad’s a milkman, he couldn’t believe it either. So I’m taking loads of pictures to send home to him.
Dennis is introduced in The Goblet of Fire:
It was Colin Creevey, a third year to whom Harry was something of a hero.
“Hi, Colin,” said Harry warily.
“Harry, guess what? Guess what, Harry? My brother’s starting! My brother Dennis!”
“Er – good," said Harry.
From HP Wiki:
Colin Creevey grew up in an ordinary Muggle family. He was the son of a milkman and was amazed to find out he was a wizard attending Hogwarts. Colin was continually awestruck at everything to do with the wizarding world. Colin had a younger brother named Dennis, who was also a wizard, an unusual thing to occur for two magical offspring to come from Muggle parents.