Your daughter should be fine, with some guidance. You're probably the best judge of what your son can handle. My nephew is very high functioning, holds a job, and can drive a car, and has been fine in a boat since he was 5-6 years old. My niece, not so much, though I depending on her mood, it might be a go. Never tried. Obviously your youngest daughter would need constant supervision. I had a rule: no kids on the decks without an adult. As always when taking kids, keep it short, expect to get zero fishing in, and make it fun. They probably only want to go on a boat ride, and see some nature.