Family and friends are sometimes your worst enemy. They can come up with a hundred reasons why not to do it. I hope that I can be the friend who say,"YA, Do it".
Life on a boat is a lifestyle that you just have to use common sense. You can not be brain dead. You have to be on you toes. So with that said, do not let your kids out of your sight. ( always a good rule of thumb wherever you are)
There are rules that have to be set and never are broken.
Our children are in their teens and are very good swimmers. But they still have a long list of rules that they do follow. Yes, life jackets, life lines, no leaving cockpit under sail, knowing how to handle radios and how to signal for emergency, and the list goes on... It is all about respecting your surroundings. I find that the kids DO NOT want to fall off the boat and are quite happy to follow the law of the sea.
We have met many children of all ages, from newborns birthed on the boat to 2-5 years all the way up to 16-18 years. You name it we have met a kid that age.