Why do the Mannings sound like they have a Different accent ??

N.O.Badboy said
Ohhh......I thought they've lived here their whole life. Especially the kids.

The kids did. Archie and Olivia were originally from Mississippi, but made NO their home after Archie was drafted here. Even when Archie moved around from team-to-team in his last 4 years or so, Olivia and the kids continued to stay in NO. Peyton, Eli and Cooper only left when it was time to go off to college. Their accents were well established by that time. All 3 boys were born in NO.

But children tend to pick up the accent of their parents to some extent and I expect that is why they sound kinda like their Dad.

Link to Peyton bio stats

Link to Eli bio stats

Additionally, here is some exchange from the posters at the American Dialect Society, not official stuff, just interesting and on topic:

http://listserv.linguistlist.org/cgi-bin/wa?A2=ind0410b&L=ads-l&P=17257

BTW, I grew up in St. Charles Parish and didn't leave S. La. until 6 years ago. But my parents were not originally from there and my accent is like my parents, not like the area. FWIW.