9th October 2017, 19:27 | Hullkr
Dagger, 18, joins the promoted Robins on a three-year contract from Warrington Wolves after the clubs agreed an undisclosed fee, while the 19-year-old Williams has signed a 12-month deal after being released by Salford Red Devils.
Dagger made his Super League debut at full-back for the Wolves at Castleford Tigers in June and is currently on duty for England's academy in their two-Test series against France.
Hull KR coach Tim Sheens, who made Leeds Rhinos captain Danny McGuire his first recruit for 2018, said: "We're really pleased to bring two promising young players into the club to complement those here who have already come through the City of Hull Academy.
"Connor is somebody I know well from our time at Salford. He can cover two or three positions in the outside backs and is really looking forward to his opportunity here.
"He's experienced Super League already and was probably a bit unfortunate not to have had more game time over there, so we're looking forward to adding him to our squad.
"Will is a current England academy international who's got a lot of potential. Again, he's already had first-team experience and we see a lot of ability in him."