Having previously denied a relationship, the two Heroes stars are now considered an item.
"Hayden's mom adores Milo. She thinks he's so cute," a family friend tells PEOPLE. "She tells her friends that he's her boyfriend. She's very proud."
On a December trip to New York City, Ventimiglia hung out with the entire Panettiere family. "He's even met her grandparents. He fits in perfectly with the family. Milo jokes around with her little brother," says the source. "They're buddies."
When the couple are together, "they're very affectionate and very comfortable around each other. He really takes care of her, even down to the little things like giving her a back massage and going with her to work things."
A rep for the actress said: "We do not respond to inquiries from the media regarding Ms. Panettiere's personal life."
'Not Afraid to Show Affection'Since cozying up at an Emmys party in September, the two had dodged rumors that they were dating – even though, by mid-November, they already were clearly close, being together publicly at benefits and other events.
When asked shortly before Thanksgiving about the reports of his possible romance with Panettiere, Ventimiglia chuckled then paused before saying, "She and I are close friends. It's only natural that people are going to couple us together."
"They're not afraid to show their affection around her family and their friends," says the friend.
As for the existence of a mini generation gap – Ventimiglia's 30, while Panettiere's 18 – the friend adds, "At first it doesn't seem like there's a big age difference, but then you do see it. ... He's more proper and reserved, and she's still playful and very girly."