Our 7-year-old has been on a number of SS cruises (starting at lot earlier than age 5) and has had a wonderful time on each of them. We've never felt out of place traveling with him (and we take him everywhere we can and as often as we can!), even on Silversea. The crew has always spoiled him absolutely rotten. And though there are not typically any organized activities for him, they almost always find something special (a board game, stuffed animal, etc) for him while onboard.
If Regent has organized kids activities, I agree that would be a bonus, but truly, my child doesn't know the difference and still has a blast. I've heard onboard previously that there tend to be more kids on the summer Alaska cruises and that the larger ships may actually have kids activities if there are enough around. We've never done that sailing, so I can't confirm.
And to respond to previous posts, yes, they do have high chairs (though I'm not sure about boosters; they used to always prop him up on a bunch pillows when he was in that size range). I think we only ever went once when he was still in the high chair phase and there may have only been one, so it seemed to follow us around to whichever venue we were dining in.