We took our 2 sons on the Holiday last summer and had a terrific time! It's a great "first cruise" ship. Some tips:
Get drink cards for the kids and you if you like pop. If you like lemonade or tea it's free and available 24 hours as well as the pizza and ice cream.
We all stayed in one cabin so we cleaned up in shifts in the morning and before dinner. Also the big closet doors, when open, make great "dressing rooms".
2-way radios for everyone let the kids have fun but still stay in touch with you. Comforting for a mom.
My sons were a little too old but your children may enjoy the kids club, great way to get to know other kids on the ship right away.
Most important tip I learned on this message board was that the Holiday is an older ship but a great size and has very friendly people. The minute you arrive (maybe even before) at the cruise terminal you are on vacation. Relax, don't sweat the lines waiting to get on the ship, or to get off at a port. Have fun and enjoy the time with your family, it is so precious.
Thought of one more idea for you. You may want to consider the sea-sick patches. We use those and never have to think about taking any pills. They are by prescription but you can go to the manufacturer's website for a coupon.