Jon Gosselin -- from baddie to good daddy?

On Tuesday, he paid a three-hour visit to cancer-stricken children at Morgan Stantley Children's Hospital in NYC, has confirmed.

"Jon is trying to get involved with more kids charities," a source tells Us. "He is very into kids and being a dad is very sympathetic to the plight of less fortunate children."

Revisit Jon and Kate's happier days

The source also slams former tabloid reporter Kate Major, who tells the new Life & Style that Gosselin used to sneak her into his $1.1 million home in Wernersville, Pa., while his kids were sleeping.

See photos of Jon and Hailey Glassman's trip to France

Says the source, "He has never been to a hotel with her and has NEVER brought her into his house or around his kids and would never ever do that. And he never planned a trip to Vegas with her. He left her a message [earlier this summer] when he was going to break up with Hailey [Glassman] and never to speak to him again and that's the last he's heard from her. She was a mistake."

See all the women to whom Jon has been linked since splitting with Kate