The rocker and his longtime love, Carin Kingsland, are expecting twins – a boy and a girl – in May, they tell PEOPLE exclusively.
"I'm so excited," says McGrath. "My DNA paranoia is kicking in: I've got to feed these children. We've got to get the nursery together. And what do you do when you bring the kids home?"
"Most parents are like, 'Oh, the wonders of child rearing,'" he says with an exaggerated sigh. "But we're freaking out! The first year is going to be gnarly."
All joking aside, McGrath says it felt "surreal" when Kingsland's doctor confirmed that not only that she was pregnant via IVF, but that she was carrying two babies.
"I love them already, but I need them to come out so I can really shower them with love," says the singer, who will host Fox's Don't Forget the Lyrics! next fall (auditions start this month) and perform with Sugar Ray this summer. "I can't wait to meet them."
New Year's EngagementThe birth isn't the only event McGrath, 42, and Kingsland, 37, an aesthetician, are looking forward to: They're also engaged after 16 years of on-and-off dating.
McGrath tells PEOPLE that he proposed this past New Year's Eve at the Viper Room nightclub on L.A.'s Sunset Strip, the same spot where he and Kingsland met in 1994.
"The first thing I said to her when I met her was, 'I think I love you,' " he says. After taking her back to the venue three months ago, he told her, " 'Well after 16 years, I know I love you. Will you marry me?' "
The wedding planning might have to wait as they get settled into family life, however. "We love the idea of getting married on 10/10/10," says McGrath, "but the twins might have another idea."