Credit: A. Macpherson/Todd G/Splash News Online

Justin Bieber and Selena Gomez toned down the PDA when the 17-year-old singer introduced his girlfriend of nearly six months to his family over Memorial Day weekend.

The couple -- who spent the last week getting hot and heavy in Hawaii -- traveled to Bieber's native Canada to spend time with his half-siblings, Jazmyn and Jaxon, and his father, Jeremy.

"They looked like one big happy family," an onlooker says. "The little kids took to Selena straight away and they were all laughing and joking around. They couldn't have been happier."

Dating since December, the pair have become increasingly more affectionate in public as of late. "I'm eighteen, and I'm going to fall in love," Gomez explained to Seventeen in May. "I'm going to hang out with people, and I'm going to explore myself, and I'm okay with that."