Kids and grand/parents to Negril...absolutely! Think 8a-9p ish days and beach rather than cliffs. Day music vs night music...etc. nothing more lovely than a 4 year old (or grand/parent) napping in the shade on the beach!
Hotels on the beach and calm water makes it perfect for the kids...room to run and wear themselves out! Boredom will not be an issue...Go for it!