Yep, USPS is the way to go. Standard shipping rates since they're being sent to an APO in the states first (Priority is 4.05$ for up to a pound)
You will need to fill out a customs forms, the small green and white if it is less than a pound and the large white form if it is greater than a pound.
There are restrictions on what you can send them. No objectionable material (ie porn), plus the standard prohibited items like tobacco and alcohol.