The portrait is unsigned and the sitters are unknown. The portrait is quite large at 115 mm x 90 mm, on a rectangular ivory plaque which is 130 mm x 115 mm. Being of this size and having two sitters, it would have been an expensive portrait when it was painted. The main image has been enhanced to pick up the color of the boy's shirt, but the other image shows the delicacy of their facial features.
Although the portrait was acquired in the New York area, the packing inside the frame includes some newspaper from San Francisco dated January 11, 1861. Thus it could have been painted in either area.
The most famous miniature portrait painter in San Francisco around this time was Thomas Story Officer (1810-Jan 1860) (aka Thos S Officer and Thomas S Officer). He worked on the East Coast until around 1850 when he moved to Australia. He then moved to San Francisco in 1855, where he worked as a miniature painter, but died as an impoverished alcoholic. Despite this, he was highly regarded in San Francisco and his obituary described him as "in all probability, the best portrait painter ever in California".
Even though the newspaper packing is dated shortly after his death, the portrait has been tentatively attributed to him. Officer did paint miniatures on larger sized sheets of ivory than most other artists, hence the large size of this portrait is also a pointer towards him as the artist. He also did tend to paint three quarter sized portraits, rather than bust portraits. In the Smithsonian American Art Museum there is a miniature of a lady that has some similarities, including its large size of 127 mm x 64 mm, see Portrait of a Lady For a large portrait by him in this collection, see Officer, Thomas Story - portrait of Dr Amos Hull
Johnson observed "To modern tastes Officer's early miniature portraits, painted from life, are more successful than his "fancy pieces", which are slick and over sentimental. During the mid-nineteenth century, however, works of this kind held wide appeal". For more about him see Thomas S. Officer
Another less likely alternative, is that they are children of a missionary, who were painted in Hong Kong or Shanghai by a local artist, as there are some stylistic similarities with items in the collection painted in those cities. 1158