One of the manufacturers sells a front hatch seat for a child. I don't believe it will be very safe for casting though. You could get a two person and just add rod holders. Ram/Scotty type. I found what I was looking for. The Malibu line sells this so your kids can come along. They seam to get good reviews as far as fishing kayaks go.
http://www.malibukayaks.com/gatorhatch.asp