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.

JJD shared the steamy snap to her 4.3 million followers on her Instagram story on Tuesday ... captioning it "Mom and Zad."

Eric rocked some red trunks and the wifey sported a peach two-piece for the poolside PDA ... and it appears like the drinks were flowing, as a half-empty glass sat on a table next to them.

No word on how long they plan to keep the Cancun party going ... so it very well could be a sandy Turkey Day for the Deckers.

The former NFLer and country singer already have a full house with Vivian, Bubby, Forrest and newcomer Denver ... and Decker did famously recently undergo a vasectomy -- but perhaps they're all getting a lil' sib in the near future nonetheless??