Ashlee Simpson and Pete Wentz at the Garfield Hundreds Pop Up Gallery

Channeling their collective inner child, spotted Ashlee Simpson and Pete Wentz at Garfield Hundreds Pop Up Gallery in Santa Monica yesterday December 9. "Pieces of Me" singer and "Sugar We Going Down" rocker both had big smiles as they schmoozed with other guests, and Mohammed is up to the press.Earlier in the day Ashlee was spotted doing some preparation for her gal pal Nicole Richie wedding