“We call him Big Kahuna,” Dunst told host Jimmy Kimmel with a laugh. “He’s like 22 pounds for a 7 month old?! My wrist is killing me!”

“All he wants to do is bounce, walk, be like his brother and walk around,” she added. “He just wants to walk and run, he doesn’t even know what crawling is.”

Never miss a story — sign up forPEOPLE’s free daily newsletterto stay up-to-date on the best of what PEOPLE has to offer, from juicy celebrity news to compelling human interest stories.

Jimmy Kimmel Live

Kirsten Dunst

TheSpider-Manactress added that she’s been sleep training James and was nearly sleep-deprived from the night before.

Dunst shares her two sons with fiancéJesse Plemons. In September 2020, Dunst and Plemons toldThe New York Timesabout their relationship, which began in 2016 when they met on the set ofFargo.

“​​We became friends and first creative partners and for me that was the beginning of us getting together,” theBring It Onstar told PEOPLE aboutworking together. “We want to do this over the course of our careers.”

As their romance blossomed, Plemons and Dunstgot engaged in January 2017. A year and half later, theSpider-Manactress gave birth to their first child together.

Emma McIntyre/Getty Images

Jesse Plemons; Kirsten Dunst

In August 2019, Plemons praised Dunst in a heartfelt speech during the actress’Hollywood Walk of Fame ceremony, which they brought Ennis to for his first official public event at the time.

“Aside from the brilliant actor you are, I’ve also had the even greater pleasure of getting to know you as a person outside of work,” said Plemons at the time. “Seeing the kind of mother, wife, daughter, sister, friend and cohort you are is why I and all of your friends and everyone else are heretoday and why we all love you. It’s for the incredibly generous and amazing person that you are.”

Despite having a lengthy engagement, Dunst told Kimmel that they’ll tie the knot “very soon.”

“I just kept getting pregnant and I kind of want to enjoy my wedding,” she joked during the show. “I just want to be able to drink and have fun.”

source: people.com