Do visit the Tunnel of Eupalinos, its an amazing achievement. Its a bit narrow at the entrance but very atmospheric once you get inside.

Try & go to the village of Manolates, if you do, climb up through the village to the last taverna (Loukas) for lunch, great food & wonderful view.
If it's still available take a boat trip over to Samiopoula, a small island with a tiny monastery on top, you have some beach time & then walk up to the top for lunch. You will have to check this is ok with a 5 yr old, it was a small fishing boat when I went that only held about 12 people, some years ago now, so I don't know if there was a minimum age.
The museum in Samos town is good too, it has the largest kouros on display (cute bum!).
A few photos of our last trip in 2008,
http://www.flickr.com/photos/yiassas/sets/72157623266089268/
Unfortunately most of the previous visits' photos have been lost with a computer crash, including the ones of Samiopoula!

great pictures. Thanks for taking the time to reply