Meanings (in the context)
"corresponde a": belongs to... (belongs to that time in the past when every girl wore laces on their heads).
"con motivo de tal evento": because of THAT (because IT WAS HER BIRTHDAY, they dressed she that way)
"la medalla": very probably, the medallion that children receive when they do their first communion (catholic religion). It's supposed the medallion is a valuable thing and the children put it on only in special events (it happened in the past, not nowadays...:)).
"Es una foto del pleistoceno": this is a hyperbole (an exageration). Pleistocene is a geological era that happened looooooong time ago. So, the writer wants to express (exageratedly) how old the photo is.
"por el cierzo": during the time of the year when this kind of wind (el cierzo) blows.
"una cara de pepona": In the past, the pepona was a famous doll with a fat round face.
"Acabamos con 10 gatos": As the Siamese cat is a Donjuan (that is to say, "a seducer") it is supposed it "knew" many female cats and, as a consequence, got a progeny of at least 10 cats. So, the sentence means, more or less: At the end, we had ten cats.