travelling in thailand with my 4 year old son!!

I am planning a 3 week holiday to thailand with my energetic, fun loving son! I'd love some feedback on my plans so far.

get to Bangkok 20 march, staying with a friend for 3 nights (what to do...lumphini park, kite flying, wats, eating? My boy is fancying the snake farm, but is it ethical...?) before heading off to Chang Mai for 4 nights. My friend will still be with us so has offered her babysitting services if I want to do a thai masaage/cookery courses. what do you think? to be honest, being given a thai masssage will be just the ticket!

we're planning on volunteering at the elephant nature park for a day. it's priced at 68 dollars for the day on the net. is it worth booking now or booking it there? we'll probably do this on the weekend.

so whilst in chang mai, apart from eating( we love our food...recommendations greatly appreciated!) and taking it all in, what else would people suggest for us? also, can you recommend any accomodation, nice but cheap/midrange?

we're then planning to move on to ko samui and spend 6 nights on ko pan gnan. any suggestions for beautiful beach, reasonable accomodation with lots of other children for my son to play with? he's very excited at the prospect of making thai friends! then i've been looking at bungalow's on big budha beach for 6 nights...has anyone stayed there... am a little concerned about air traffic noise.i like the look of the bungalows at secret garden, that's 2000 b per nighthich i'm willing to pay, but could do with paying less! and am concerned it'll be full of honey mooners who won't appreciate my son's wanton abandon!...any other suggestions?

all info/sharing/ and reading this ramble, much appreciated!