Eric and Jessie James Decker have four kids, but don't be surprised if another pops up in nine months ... as the two couldn't keep off each other during their Mexican vacation -- and they wanted everyone to witness it all.
The married couple -- who welcomed their boy, Denver, in February -- are on quite the hot streak while south of the border ... and even though it's a family trip, the two made sure to sprinkle in some romance along the way.