Using a instead of para

Question

In the exercise the phrase 'Haciendo la compra a mis mayores' is used. I would have expected 'para mis mayores'. Is the use of 'a' instead a common Spanish usage?

Answer

Hola Anthony
Yes, you can also say "para mis abuelos" with exactly the same meaning. Sometimes we use "a + person" as an indirect object, the same way we would say for example:
Le compré unas flores -> Compré unas flores a María -> Compré unas flores para María
It doesn't work with all verbs that use an indirect object with "a" - for example, you can't say "Le dije una cosa para Luis" (meaning "Le dije una cosa a Luis". But with "comprar" you can. 
Saludos
Inma