David Wells says Marshawn Lynch is dead wrong for cussing at kids during his football camp last month ... telling TMZ Sports, "You gotta be more a little more professional than that."
We broke the story, Marshawn was out at his Fam 1st Family camp in the Seattle area on July 28 ... when several kids -- some as young as 9 years old -- broke down crying because he swore at them while making them run laps.
In video obtained by TMZ Sports, you can hear Marshawn admitting to using the f-word and the n-word toward the kids in an intense confrontation with some of their parents.
When we got Wells out in NYC over the weekend ... the ex-MLB great told us the whole ordeal wasn't cool -- saying Lynch should watch his language around kids so young.
"You're trying to set an example, right?" Wells said ... "You don't use that around kids -- you gotta be more a little more professional than that."
Wells says he practices what he preaches ... saying if he catches his owns kids cursing -- he washes out their mouths with a bar of soap.
As for when he thinks it's appropriate to cuss -- Wells says that bar starts somewhere in the teenage years.
"As long as they don't use it around the table or the house," Wells says, "then you're good."