A sense of humor is very necessary with children either ashore or at sea.
Child size safety equipment.
Assorted toys & games that they really enjoy... Don't carry anything that they don't want to play with. And keep those to a minimum if you can get away with it...
Lots of reading materials for them.
The top of the
line First Aid Kit. Along with the training necessary for it.
First Aid training for Sea-Going personnel is much more intense than the basic Red Cross First Aid training course. It is more on par with EMT's skills.
The appropriate clothing for the weather you know that you will encounter in your voyages. But keep it basic as much as possible.
Did I mention Child size safety equipment?? Be sure that their lifejackets &
harnesses are comfortable for them to wear. and when they are in the cockpit or on deck, always hooked up to a jack stay
line.
Netting along the lifelines. To make it harder for people to go over the side when at sea.
Look into home schooling. So they may keep up with their peers in education. Calvert(?) has good courses for children voyaging with their parents.
I'm sure that there are other items that I have missed but some one else may have a better input on this subject.