The boat market does not forgot about kids, there are several kids boat models that are extremely fun for the little ones, most of them are inflatable and are designed to bring comfort, color and fun of course. Obviously these models are just for floating and playing on a swimming pool, nevertheless security equipment is always recommended both on a kids boat or on real ones.
When you travel on a real boat with kids security becomes even more important, for example the Australian government enacted two laws that began functioning from 1 November 2010, they say:
From 1 November 2010 children under the age of 12 years must wear lifejackets in the following circumstances:
As you can see, those are good regulations, so take a look at the regulations on your own country and in case your country does not have them, you can apply the Australian. Kid's skin is also different and more sensitive than adult's, so it is very important that they wear proper clothes to not suffer sunburns, as well as hats, sunscreen and sun glasses.
It is also very important to teach your kids to behave inside a vessel, they should keep all the body inside the boat as long as it is moving, and avoid playing and running, also teach them to use their lifejackets and what to do in case they have an emergency, if they are old enough to understand what you say, you can explain them how to handle some tools like the radio, flares or lights, indicating how important they are and the fact that they can use them only on emergencies.