These children have the surname Sobol, so it's fair to assume they're related to my great great uncle in some way.
This caption is longer than the last one. There are two words underlined; those are the names of the children.
Natalie interpreted the caption as follows:
"This is Mixaylo (Michael) Sobol's children. First it's [looks like] Zdaco and the other is Stashko. This picture came with the letter."
Sobol had a brother named Thomas, who I think stayed in Ukraine. These may be his grandchildren.
Next -- Old folks and a wedding, 1959