Just looking for any recommendations on paperwork/preparation to allow my daughter (2 years old, with both Thai and US passports) to be able to travel abroad with her grandparents (they are both Thai but grandma holds a US passport as well).

I've prepared a generic form outlining permission that my wife and I will both sign...do we need to get it notarized? Is there such a thing in Thailand?

No issues with trust here, just want to ease any immigration/security check situations they might have.

Thanks in advance guys.

As far as I know you will need the mother's consent and if its ease of passage you are after then I strongly suggest both you and yourself be present at the airport to explain the situation to staff. Even travelling by plane within Thailand is a little problematic but abroad and neither parent travels, well I don't believe you will be given passage without both parents being present and being able to show that you are the parents (eg, passport) abd are giving consent.

When we traveled to Phuket, this is what Thai airways insisted upon, no notarization required but that was an internal flight and as the father I was with my child, so its a different case to yours. Obviously the worry from officials is child abduction and they must take as many steps as they can to minimize it.

You can have it stamped by the amphur and should include a copy of both your ID-cards/passports. Might also be handy to give the granparents permission to make decissions regarding the child. That will practically only be needed if the child gets an accidents, than the parents or guardians must give permission for any medical procedure that is not life threatening.