I'm old fashioned and / or maybe just lucky too. My wife and have been on 35 or more cruises and I've never lost her yet, nor has she lost me, at least not for any length of time. Just make some prearranged meeting places and times--you don't need to know every time someone gets out of your sight where they are--in the bath room, trying to get a few minutes by themselves, trying to get a nap, etc.
There is such a thing as spending too much time with traveling companions and on a ship it can very quickly get to that point.
If you have kids, what do you do with them at home? On a cruise, do the same as you would with adults--have pre arranged meeting places and times and expect them to be there. You may be on a cruise with your kids but they're still your kids and you are ultimately responsible for them. If you have a walkie-talkie and try to keep up with them that way, they can tell you anything they might think you want to hear and be nowhere near where they say they are. Ships, regardless of how big people seem to think they are, aren't really so big you lose people indefinitely with just a smidgen of common sense. I've traveled with groups before and sneaked off many times to get some down time and away form the crowd. You couldn't law one of those walkie-talkie thingees off on me on a ship.
Gotta have my space and time.