The two took their son Bronx, whom they welcomed last November, to the Elizabeth Glaser Pediatric AIDS Foundation's "A Time For Heroes" celebrity carnival in L.A.
As Pete helped locals customize T-shirts, Ashlee stood by his side, making faces and smiling at Bronx, whom she held in her arms. One of her pals grabbed a white baby top so Pete and Ashlee could make a T-shirt for Bronx.
Pete -- who celebrated his 30th birthday Saturday at the Bank nightclub at The Bellagio Las Vegas -- also was on daddy duty at the event, holding Bronx as Ashlee chatted with some fans.
Ashlee began cracking up when a young girl approached her for an autograph and Bronx tried grabbing the girls autograph book.