David Wells Says Marshawn's Wrong For Camp Cussing, Don't Swear Around Kids!

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.