The most prominent and undoubtedly most important theme in the poem would be the love, affection, and appreciation the speaker feels toward her family.
Looking at an old photograph, she begins to recollect the past days of her childhood spent with her brother and grandparents, setting up the scene and imagery in her mind as if she is reliving the moment. She fondly remembers the quirks and personalities of her closest family, describing her brother as follows:
His Davy Crockett cap
sits squared on his head so the raccoon tail
flounces down the back of his sailor suit.
Here, she seems to be painting him as an exuberant boy full of youthful energy.
In the last verse, she mentions that she remembers her grandfather's smell and his hands. She uses nostalgic, and maybe even elegiac, language, writing:
I was strapped in a basket
behind my grandfather.
He smelled of lemons. He's died—
but I remember his hands.
This is noteworthy, because throughout the poem she presents small and banal details that would be unimportant and uneventful to any other person, but to her they are some of the warmest and most endearing memories she has of her family.