We signed up for a world cruise, before Covid threw a wrench into our pans. We would have been away now. 120 days, LA to London. 40 ish ports, mostly arrival in the early morning, breakfast aboard, tours during the day, dinner aboard, gone at dusk.
For a 6yr old kid, you wouldn't get this kind of cruise, as the cruise line is set up for an older demographic. 2 per room, nobody under 18 aboard, those 18 to 55 all still working, so mostly older, retired folks (like us).Entertainment consists of music, lectures, hobby stuff, reading, etc, so nothing for kids. No casinos, no waterslides, none of those things that are designed for that demographic and won't work on a smaller passenger base.
At the other end of the spectrum, if you have your own boat, can do home schooling, I know of families that have spent 4 to 10 years cruising around the world and have given their kids a very special upbringing. It can be done, but you need to look for the advice of a very different group.