A few ideas from a lake sailing grandma...
PFDs on before you set foot on the dock, the whole family (set example). They stay on except below in great weather. Our grands got used to them (reluctantly). A safe corner, visible from the cockpit, with "car toys" (stuff that travels and can be played with while sitting). This would be mostly for the older child, but you could set it up with a space for the younger one as well. Go out early for short sails to be back at dock for nap to help the little one adjust to sleeping on the boat and let Daddy give Mommy a break.
And, yes, get a sitter occasionally! Your wife will probably not make any progress in learning when she has her mind on the kids.