Bigbad, I used to love Tradewinds on Chaweng Beach.
It's gone somewhat upscale now from when it used to cost about $20 a night but the location and leafy surroundings offer an oasis for a family.
http://www.tradewinds-samui.com/
Next door was the huge Central hotel. Head over there with your young one for a swim in the pool. :)