Richard Pryor's Kids -- Nick Cannon Can't Play Our Dad!

Nick Cannon seems to think he has the role of Richard Pryor locked up for a new biopic ... but Pryor's kids tell us they don't think he cuts it ... but they say they know who can.

Richard Pryor Jr. and Rain Pryor say the man for the role is Marlon Wayans. They believe Wayans understands their dad's psyche and can connect with the character in a compelling way.

As for Nick ... they just don't think he has the acting chops to pull off the role. They say "Drumline" doesn't give him the cred to play Richard.

But the kids have a more fundamental problem with the biopic ... they tell us it dishonors their dad because it's become a vanity project for their stepmom, Jennifer Pryor, who they believe will skew Richard's life to make her look good.

The kids are also clearly pissed they've been cut out of the project.

This may explain why Nick was kind of coy on TMZ Live Wednesday ... reluctant to acknowledge if director Lee Daniels has tapped him for the role. It seems he wants his participation to fly under the radar, so the family doesn't kick up dust and scare the studio.