Now that's one proud papa!

Joel Madden spent a sunny afternoon outside with his two tots -- daughter Harlow, 2, and son Sparrow, six months -- and couldn't get enough of their sweet sibling love.

"My new profile pic," he Twittered Thursday after sharing a photo of Harlow hugging her baby brother, who wore a blue onesie with ships on it. "It causes smiles."

He added: "My kids are the best."

The rocker, 31, also gave a Twitter shout-out to his fiancee Nicole Richie, who took over his account on April Fool's Day, which also happens to be the anniversary of the birth of his band, Good Charlotte. (She wrote funny messages to the likes of Ricky Martin, Paula Abdul and Ashley Tisdale.)

"Soooooo should have known Nicole would hack my twitter on April Fools," he wrote. "She hasn't even said Happy Bday to GC."