Hi.
Im sorry for taking so long to get back to you.
I dont know those hotels that you have mentioned but try and get some reviews on trip advisor. They are normally very honest and to the point.
Siam park is fantastic BUT i would not recommend it for a 3 year old as it is more for the older child, maybe 6 onwards.
However, there is a little area for the smaller children, little slides etc for them to play on.
There is a big pool in siam park but it has a wave machine and even if you are in the shallow part it can be tricky to keep balance.
There is another waterpark here called 'Aqualand' and to me, i find it much more child friendly as you have a big pool but with no waves so you can enjoy a swim and not get draged under water.
A few of the rides you can actually have children with you as they are tamer.
The best thing though is they have a dolphin and sealion show at 3pm which is a really teriffic show.
Also at aqualand you can purchase another ticket for just 5 euros for another day so you can go back and relive the fun without having to pay top whack.
Sorry for blabbing on there,i have just realised how much i have written hehe.