Her son Bronx Mowgli, now 4½, is becoming a “smart, sweet and amazing” little boy, she says.
“He’s always funny,” Ashlee, 28, told PEOPLE at the launch of older sister Jessica Simpson‘s fall fashion line campaign at the Thompson LES Hotel in New York.
“He keeps you on your toes and he’s got great stories and a great imagination. When I was doing Chicago, he said he was making his own play about ninjas.”
Bronx (whose dad is Fall Out Boy rocker Pete Wentz) has also taken on the role of doting cousin to Jessica’s children, Maxwell Drew, 14 months, and Ace Knute, 4 weeks.
“Oh he loves it. He’ll get it soon. Right now, he’s like ‘OK, Maxwell, come hang out with me! Let’s go to your play room,’ ” she explains. “We are always all together. We’re a close family.”
As for how Ashlee celebrated her newborn nephew’s arrival, she opted for a sentimental gift when he was born on June 30.
“There was this awesome thing that we made with Bronx,” she explained. “It was like cool, vintage shirts all made into a blanket, so all these things that represented his mom and dad. So we made that all into a blanket. Just cute stuff — things that represent Eric, things that represent Jessica, and you take the little vintage shirts and jerseys and make [them] into a blanket.”