Watkins, who is Welsh qualified, has scored a blistering 51 tries in 87 appearances for Bristol - including 39 in the league to make him the club's joint leading league try-scorer.
Jenkins, 20, made his Blues senior debut this season in the RaboDirect PRO12 draw with Benetton Treviso in November.
The flying Wales Sevens and Under-20 international wing, son of former Wales hooker Garin Jenkins, has shone for Pontypridd RFC in recent seasons and has now agreed a three-year contract with Blues.
Director of Rugby Phil Davies was delighted to bolster the firepower at Blues by agreeing deals with the two young Welsh hot prospects.
"George and Owen are two talented young Welsh players who will be important for the Blues for years to come," he said.
"I've known about George since my time at Worcester Warriors when I tried to sign him. I have followed his progress for the last four years in the English game and he is a prolific try scorer in a competitive league.
"Being Welsh qualified I knew he was keen to come to play in Wales and he's a young wing who will thrive in our system. He has an excellent attitude and is keen to get started.
"Owen has really impressed in our Academy, made his debut for us this season in Italy, where he played exceptionally well, and is one for the future," added Davies.
"He has been involved with the Wales Sevens so has great footwork, is a good defender and scores tries.
"Owen comes from a good rugby family, as I played with his father, and I know he will only get better during his time with the Blues. His potential is clear for all to see.
"It's exciting for us to sign up two talented young Welsh players on long-term deals and I now look forward to seeing them both impress in the coming years."