If you are looking for kayaking, I highly recommend Dean Livesley at Seven Capes. A lovely guy, good equipment and a range of trips from morning paddles to three-day coastal treks!
I don't know if this would work for your family, but in August his night-time paddle during the Perseid meteor showers is fantastic. Very easy to do and he even has a couple of double kayaks, so an adult could go with a child. There are a couple of swim stops, a picnic tea and you get to watch the meteors and experience the bio-luminescent particles in the water - amazing. Did it last year and probably will this summer too.
This is his website -
http://sevencapes.com/ 