Hi Wayne,
I think that it is great that you folks are taking the time to bring in kids.
A couple of thoughts...
Your approach should depend on the age of your honorary member.
First through about fifth grade, kids are sponges... being very creative and wanting to try everything. Just the opportunity to play with things which might be a "chore" or "challenge" to parents at home, like getting to slap paint on something can be a real charge to a kid this age. Also at this age, the process is going to be more important than the result, so make it fun. Ask them "What would YOUR pirate ship look like?" Also, they may not have the manual dexterity to deal with assembly of smal pieces. I would recommend a relatively large, simple kit with lots of open deck space, like Revell's Santa Maria or Mayflower. Any such vessel could be a pirate.
Don't loose track of the fact that a kid's most likely interest is in pirates, not pirate ships. A larger scale model will provide the opportunity to populate it with pirates. Begin and end sessions with work on a pirate figure or pirate paraphenalia, like cannons and swords. Obviously 1/96th scale is not going to work well.
Don't fret about historical accuracy or scale. On a larger kit, just focus on fitting the largest pirate figure that you can in the space. And forget rigging... a few strings will do, especially if it includes what we older folks would call a "Tarzan rope", or in sailor parlance a "splat line".
For younger kids, you might consider pre-assembly of components and allow them to focus on larger sub-assemblies, painting and placement of figures. Also, having a basic hull/deck assembly available, even if it is just taped together is a great stimuli. Letting them see their figures on board, painted and unpainted gives them an opportunity to see the transformation/ progess as they go.
Balancing subassembly time and limiting total project time is critical at this age. Since you are working with an individual, you can tailor your approach to the kid's age, motivation and abilities.
Around fifth grade, or older, manual dexterity and interest level can lead to a simple scratch built vessel. Again, it needs to cater to their imagination, not interest in historical accuracy. A good example for a simple scratch build is an ancient Egyptian Nile river barge. It can be as simple or as elaborate as the modeler's interest inclines. and provides much appeal to the imagination (funeral barge with painted sarcaphagous on deck - or Cleopatra and her maids?). Reference material for Egyptian decoration are readily available, and since there are not many records of what the vessels looked like, reduced pressure for "historical accuracy". A simple hull can be carved from a balsa or soft wood block. A single mast with a single square sail is simple to fabricate and rig. The sail and the hull require decoration with opportunities for phased, discrete, simple operations. A relatively large scale provides opportunity for populating it by modifying commercially available figures.
Anything that I would do would cater to the following objectives, which should all trump OUR modeling objectives, ie. historical accuracy or showcang OUR modeling skills.
1.) remember that we are contributing to the raising of ADULTS, not children. Our objective is not to create a museum quality model but to develop skills and constructive attributes and habits in our young wards.
2.) patience is grown, bit by bit. Modeling provides the opportunity to develop this important attribute. Today, it has to be teased out of children, not forced. Today's environment is focused on short duration visual stimulation and, other than game controls, offers little opportunity to develop manual dexterity. Break down the project into phases, starting in short sessions, for younger kids, perhaps no more than fifteen minutes or so. Start and end the sessions by stimulating the kid's motivation to participate. Your objective should be to extend the kid's attention span, and work session duration over time.
3.) Always remember that positive reinforcement is critical. Resist the temptation to be the "master". That comes later, when the kid has developed the wherewithal to really appreciate the quality of your work. Too high of a standard will be discouraging in the early phases. Don't be afraid to lay on the praise.
4.) Stress safety and good, organized work practices. These things are ingrained by repeated supervised, "doing", not learned from lectures. Realize that you may be the only source of how to approach the use of "hazardous tools and materials". This presents an opportunity for you to review your own practices in using sharp objects and volatile solvents... try to avoid passing on bad habits. Supervise everything and consider age and individual capabilities - Don't be afraid to correct bad or dangerous practices - at this level, the development of skills and safe practice should be your primary objective and concern, not historical accuracy.
5.) Work to develop inquisitiveness and forethought. Don't make all of the decisions, or attempt to instruct on the fine points of rigging shroud lanyards. Again, throw historical accuracy out the window for first projects and develop the interest and lay the foundations for basic research skills over time. Hopefully you can locate references at a local library and steer your young modeler to them after he or she is "hooked". Ultimately, learning and practicing basic research and planning skills may be the most benefical impacts on a child's life.
6.) Be aware of the crazy litigous world that we live in. It is always a good idea to have other adults (preferably including the kid's parent(s)) present when working with someone else's children. Be aware of legal requirements for background checks, etc. for the circumstances that you are in. Be aware of your liability insurance coverage - is it through your homeowner's insurance or is it through the club? Can you work this through a local scout troop or similar organization that can provide such insurance? -- What will happen if your young modeler gets a nasty cut from an X-acto blade? I'm not qualified to give legal advice, but remember - What you are doing is very commendable, and important - but as they used to say at sea - "one hand for the ship, one hand for me".
Again, I am glad to see your club take the initiative in this area. Good luck with your endeavors.