Depends on how much you want to spend. A Hobie 16 is your cheapest option, but has drawbacks:
1. 4 people don't fit well on an H16.
2. It isn't very forgiving in wavy and harder wind.

The best family boat around is the Hobie Getaway. It is forgiving on all points of sail. You can easily fit 4-6 people. A 2-person crew in medium to heavy wind, the Getaway is just as fast as a Hobie 16. No boom, furler for the jib, built in coolers, same weight as a 16.

The Getaway has been around since late 2000 so used ones are hard to come by, that would be the big drawback.