started in a canoe, they can lay down in the bottom when tired and we could take a cooler full of food and drinks. As they got more interested we could talk about reading water and I'd let them pick lines through rapids. By 7/8 years old they moved into their own boats.
We also spend lots of time swimming. We're about and hour from the Chattooga and would go and swim in the run out at Bull Sluice and Woodall. It got them used to swimming in moving water.