I messed up my response.
Your comment about your son having reservations likely gives you the answer.
I’ll add that we started traveling with our son at 3 months old. While we didn’t sail, we did trips that otherwise had our friends saying we were crazy.
There are two key factors to consider -
Child’s temperament - we are blessed with a child who is “chill” for lack of a better word. Even as an infant, we could take him anywhere and he was happy to nap under a palm tree, slept great in strange beds, eat off our plates when he started solids, etc.
Parents attitude - my husband and I were on the same page. We knew we wanted to travel and made the necessary accommodations to make it a great experience. We worked as a team. No bad attitudes because one adult was bitter about not being able to sit at the bar for three hours, wanted to sleep til noon or whatever.
OP - my advice is to give serious consideration to your DIL’s attitude about this trip. Is she excited or is already thinking about everything that will go wrong? Is she the type that will freak out if nap or mealtime is 5 min late? Those types don’t travel well in my experience.
