ET's Cameron Mathison caught up with the star at a screening of his new film Love, Simon at the Westfield Century City cinemas in Los Angeles on Tuesday, and he opened up about how he's helping to make sure his son becomes a tee-ball champ.
"We have full on practices at the house," Duhamel shared, adding that he's training his 4-year-old son "like a dog."
"I'm putting little pieces of candy at each base, if he hits it past me he runs to first base," Duhamel said, laughing. "He has no idea [he's training], he just wants the candy. But he's learning how to hit, I'm making him hit from both sides of the plate."
For Duhamel – who shares his little boy with his ex, Fergie – getting to teach Axl to play ball has given him a real understanding about fatherhood.
"This is why I wanted to be a dad," the 45-year-old actor said. "[It's] to be able to have moments like this with him."
'Love, Simon' Is a Modern-Day Coming Out Story -- Watch the Trailer
In his new family dramedy Love, Simon, Duhamel plays the father of a teenage boy who is struggling with his identity and with coming out as gay. The role allowed Duhamel to channel his own experiences as a father, and he says the film will have a positive impact on families that watch it.
"I think anybody who's a parent will understand that no matter what, no matter how unexpected the surprise, that you love your kid," he shared. "I think that it's about acceptance, it's about tolerance, at the end of the day it's about being a kind, compassionate human being."