Was HNL two levels in 1961?
I suspect they are both leaving and she is 3 months pregnant. If they were both leaving after Baracks birth she would be holding Barack. If he was leaving on his own, after Baracks birth, she would still be holding Barack. There is nothing that I have read or seen that would indicate Barack Sr left pregnant Ann to go home to Kenya.
In reading in the Time magazine she met Barack Obama Sr. in a Russian-Language class. I presume she started in the Fall when school usually begins. Then later in the article it says "At 18, she dropped out of college after one semester, according to University of Hawaii records. When her friends back in Washington heard the news, "we were very shocked,"
This leads me to think it was because she was pregnant and the two of them Barack Sr, and her then went over seas as is seen by the two of them at the airport.