Matt, would you always be boating with both kids, and your wife?
In that case the above posts advancing the 22' are very sound. But if you were to, say, devote a special day to one child to go boating with dad, I'd have little fear that the 16 would provide very adequate safety.
Pick the right day, motor around Gig Harbor, maybe out along Colvos Passage, perhaps up to Blake Island for a hike. The kids will never forget the wonderful moments you will have created.
Make sure they wear their life jackets, are respectful of the potential danger, know how to swim and understand why they can't run around and go wild. (One has to be 51 to do that.)
Too, a sunbrella camperback enclosure is highly recommended.