Olivia Wilde shared a rare photo of her 11-month-old son Otis via Instagram on Wednesday, April 1

My kind of party.

A photo posted by Olivia Wilde (@oliviawilde) on Apr 1, 2015 at 10:23am PDT

Baby Otis must be really excited for his birthday! Olivia Wilde shared an adorable, and very rare, photo of her 11-month-old son via Instagram on Wednesday, April 1.

"My kind of party," Wilde, 31, captioned the snapshot. Getting silly on April Fools' Day, the makeup-free mom mimicked Otis' funny expression.

The blonde tot was cute as a button (but, of course!) in a gray sweatshirt and "Red Airplane Clouds" bottoms by Doodlepants. The Meadowland actress, meanwhile, wore a blue cable knit cardigan as she crouched on all fours so she was face-to-face with him.

Wilde and fiancé Jason Sudeikis, 39, welcomed Otis in April 2014. In February, the O.C. alum shared some of Otis' milestones during an appearance on the Today show.

"He’s about to walk. He’s teetering and I just don’t want him to do it while I’m at work,” she said, adding: "He’s so smart and just plays his piano all day long. He’s really musical so we’re trying to encourage that."