I've been on two cruises, one with my 5yr old DSS.
Personally, I thought it was a waste for DSS.
Cruises are great for adults, loads to do, sightseeing at every port, great food and entertainment.
With DSS, it was a little fraught, he wasn't interested in sightseeing obviously, wanted to eat in the burger/pizza restaurant every night.
Couldn't take our eyes off him for 5 mins as he was obsessed with looking over the rail, it was pretty stressful.
The days where you sail all day were horrendous, no-one can get off obviously so it's really busy, you can't get near the pool, all restaurants are busy, queuing for a drink etc
Dss was constantly "bored" on a holiday that cost an absolute fortune 😃
Couldn't have a cabin with a balcony as he wasn't old enough, I think the dc had to 10 yrs old, inside cabins were dark and gloomy.
This isn't a stepchild bashing post, I love DSS and been on countless holidays with him, he was just a little boy who was into everything (grown up now)
I'd save the cruise until your dc are off to uni and you and dh can go alone.