Santorini has a few very interesting places to spend with your family and below are some of them:
http://www.santoriniwaterpark.gr	http://www.divecenter.gr	http://www.santorinidiving.com

Also look for the Paint Ball facilities in Megalochori village which unfortunately doesn't have a website but it is lot's of fun playing! You can reach them by phone at  +6942442399

...and of course many water sports activities in every beach!