EXCLUSIVE

Rhett McLaughlin -- one half of the famous YouTube duo Rhett and Link -- just expanded his family ... by a couple of pounds.

Rhett and his wife Jessie got a maltipoo pup named Lola from Wylder's Holistic Pet Center and Rescue in Studio City, CA.

Sources at Wylder's tell us Jessie came in last week by herself at first, but immediately fell in love with Lola and called Rhett to get over there with their sons, STAT -- and sealed the deal on the spot.