The former Saturday Night Live star spoke to ET at the premiere of his latest film, The Devil and the Deep Blue Sea, at the Tribeca Film Festival at the John Zuccotti Theater in New York City on Thursday, where he joked that Otis, who turns 2 next Wednesday, is the mastermind behind the special celebration, coming up May 8.
"[Otis] has got all sorts of stuff cooked up," Sudeikis, 40, joked. "But he won't let me know because he doesn't know enough words yet!"
Coincidentally, Sudeikis stars in the upcoming Garry Marshall movie Mother's Day, which hits theaters April 29.
In The Devil and the Deep Blue Sea, Sudeikis stars alongside Jessica Biel, who also served as the film's producer, and Sudeikis had nothing but praise for his 34-year-old co-star and boss.
Sudeikis recalled how Biel made the initial contact back in 2009, sending him a script and "a lovely letter that accompanied it."
"She answered my No. 1 question which was, 'Why me?' She was very sweet about that," Sudeikis recounted. "She stayed the course and I think she did a great job."
In the film, Sudeikis plays Henry, a mild-mannered architect whose life is devastated when his wife Penny (Biel) is killed in a car accident. Afterward, Henry tries to heal by helping a homeless teenager named Millie (Maisie Williams), build a raft that she hopes to sail across the Atlantic.
Despite the intense drama inherent in the film, Sudeikis said he managed to keep his head up with visits from his 32-year-old fiancée and their son.
"They were there [on set] at least for two of the six weeks," he recounted, adding that his iPhone was very helpful when they weren't around, as he would look at photos of his family whenever he missed them.
The Devil and the Deep Blue Sea is set to hit theaters later this year.
For more on Sudeikis and Wilde's adorable little boy, check out the video below.