We don't travel that much, so having kids hasn't interrupted it, though
with international moves we've done more than we expected.

We took DS to Cyprus (from the UK) aged 10 months, it was no more
difficult than a domestic holiday, though in the UK a domestic holiday
doesn't involve flying and UK to Cyprus is closer than East to West
coast of the US!

We then took him to Korea aged 18 months, which was a short term move
rather than a holiday, from there we took a holiday to Guam, again, a
non issue.

Had another baby and left DS with grandparents and took a week long trip
from the UK to Seattle with her, hard work, but again not a biggie.

We then moved to Seattle and have only travelled within the US, though
my parents did take DS to Whistler, again, they found it more tiring
than travelling alone, but really enjoyed it, they put him in kids club
two out of the three days they were there and enjoyed spending a day
with him and I think he enjoyed it too.

You obviously know cruises, I've never been on one. I do remember going
on long ferry journey's as a kid and finding them boring, but then a 24
hour ferry journey with nothing organised is a different ball game to a
cruise, where it's supposed to be for pleasure itself rather than a
means to an end.

I think the main thing is the type of accomodation you have, some kids
are ok with sleeping in the same room as the parents and will fall
asleep no problem and sleep well, others won't. DS is fine, DD isn't,
the price can be a lot different on a cruise depending on which option
you need, so if you don't know which your DD is like, a test one night
trip to a motel might be a good idea!

Cheers
Anne