Pete Wentz's son wants to ''punch'' his next birthday cake to prevent himself from growing up.

The Fall Out Boy bassist revealed four-year-old Bronx, who he had with ex-wife Ashlee Simpson, is so determined to remain forever young that he plans to ruin the sweet treat when he turns five in November with the hope it will stop him from aging - an idea that Pete finds ''genius''.

He said: ''[Bronx] is definitely at an age where the imagination and the reasoning are just firing on a level [I can't understand]. I don't know if I ever had an imagination that good...When he's describing things or saying things, it's mind-blowing to me.

''He was like, 'I don't want to be grown up.' He's like...'On my next birthday, I'm going to punch my birthday cake.' So he doesn't have to grow up. But I'm like, 'That's genius!' He doesn't even know how amazing that is! I'm like, 'You should punch your birthday cake! It's your birthday! Do it!' ''

Although Pete, who is currently dating 24-year-old model Meagan Camper, loves how imaginative his son is at this age, he expects Bronx may grow up to ''rebel'' the things he has grown up around, including his dad's tattoos.

He added to Us Weekly: ''The thing that I've noticed is a lot of kids tend to rebel against whatever exists [in their own families].

''I have friends who are in bands, and their kids are like hippies or whatever. So [Bronx will] probably be into math and be like, 'I'm not into tattoos.' And it's like, now I've got to figure out how to really do some of this essential math.'''