Both my son and daughter used a Sea Flea up to 55 lbs. Without an issue. She actually paddled it with the water about 1/4" from the back deck top just for fun. Only capsize was when she backed under another boat. She has flipped her Sea Bee many more times already. More adventurous.

For a small kid size sea kayak it appears very stable within its weigh range. 7-8 year old would be maxxed out. Put them in it on a line for a few minutes on a calm lake, then went for a paddle.

https://picasaweb.google.com/117559716817437712203/11FtSeaFleaKayak

Ithink the pic says it all.