Wow, 6 nights at Amantaka and Amansara each, we are extremely jealous
Perfect choices of activities for Amantaka, I believe your son will really enjoy the experience at the bear sanctuary.

For Amansara, if it's your first time in Siem Reap, the "must-dos" are Angkor Wat, Bayon and Ta Prohm. We have visited Siem Reap a few times and found Ta Nei (a small temple on the outskirt of Angkor Thom) offers a much quieter and jungly feel. Sunset at Bayon is a magical experience

The team at Amansara will time your visits to avoid the crowds, unfortunately that means 5am wake up calls in the mornings and after 3-4 days "temple fatigue" sets in...
I would perhaps take one or two day off from the outings if you have 6 nights. A traditional breakfast at their Khmer house is a great alternative to house outings!

The Tonle Sap cruise "Amanbala" has been launched for about half a year I think, from what I heard from Sally, guests feedback has been amazing. We have yet to try for ourselves though, may be until Feb next year