I've long though it was odd that Obama Sr, who hadn't really met Obama Jr in the 10 years since his birth, flew nearly 11,000 miles from Kenya to Hawaii for a 10-year class reunion Univ of Hawaii. Obama Sr had graduated from U of HA in May or June of 1962, 9 1/2 years earlier. Coincidentally, that's just when Ann briefly traveled to Hawaii with Obama Jr from her home in Jakarta with Lolo. She just happened to be there in Dec 1971 while Obama Sr was there. Ann was there to drop off Obama Jr to stay with his grandparents while he attended school in Hawaii away from his mom, step-father and baby sister Maya. Or perhaps, Lolo was there in Hawaii after all during that time to sign paperwork ... who knows.
The Indonesian school records seem to indicate Obama Jr had already been adopted by Lolo Soetoro in 1966 or so.
It was "decided" that Obama Jr would live with his grandparents in Dec 1971. The marriage between Ann and Lolo doesn't seem to fully hit the skids yet based upon Ann's statement on the 1980 divorce request: "husband and wife are not legally separated but have lived apart by mutual consent since Aug 1974."
So, an American (Hawaii) adoption or Obama Jr by Lolo, who was an Indonesian with a name change involved to Barry Soetoro, seems like a very likely scenario. Of course, we don't know that for sure since the Obama Jr/Barry Soetoro is not specifically named on the 1980 Divorce request other than as "1 child above 18 but still dependent on the parties for education."