Olivia Wilde had a disastrous first Mother's Day.

The 30-year-old actress was left disappointed when her plans to celebrate the special family day this year with an idyllic brunch in New York City's Central Park were ruined by her two-month-old son Otis pooping like ''a torrent'' all over her and her fiancé Jason Sudeikis.

The 'Rush' star recounted on 'The Late Show with David Letterman': ''I had the image of the picnic and everything would be so lovely. There would be flowers and the baby would be cooing and I would be the glorious mother.

''Instead, we were sweating, and angry and hungry. Everyone had to pee. I finally just dropped to the ground on a patch of dirt, like in between two ugly roads, and then just ripped off the diaper of the kid to change him and he just pooped everywhere - like a torrent, a flood.''

On top of Olivia having to deal with so much baby faeces, the day was marred by her poor sense of direction and inability to find the park's bathrooms.

She said: ''I had this image of Central Park being completely empty, just rolling meadows, one person a mile away flying a kite, some balloons. So he says, 'Yeah, we can do that.' So we go up there and it's hell. It's more packed.

''Everybody in the world is in Central Park that day. It also happened to be Japan Day, which it turns out is a huge deal in New York City ... There were, like, a billion people there and there's one bathroom, as far as I can tell. Maybe there are more - I couldn't find it. It was a bad decision on my part.''