If you must paddle a two-person kayak, solo you will want to sit in the middle seat, if it has one, or the back seat. You will have the best control of your boat by sitting in the middle, good control if you sit in the rear, and poor control if you are in the front seat. You can put a load, such as a cooler or a dog, in the front seat to balance the boat. When paddling with children you will want to seat them depending on certain circumstances. Very small children are best seated in the lap of an adult.
Larger children ride best in their own seats or a suitable storage well on the deck.
In a three-seat kayak, with a party of two adults and one child, put the adults in the front and back seats and the child in the middle. This allows for either adult to attend to the child. If you are one adult and two children then you may put the kids in the front and back seats while you control the boat from the center seat. Putting the children in the bow and mid seats while you sit in the rear helps trim the weight in the kayak properly. Some times you can put two small children in the same seat.