"Do you often write your parents?" is also a valid translation of this sentence. What we have here is an instance of what can be referred to as the dative case, and the word "to" is not needed to express it in this sentence.
This is something we hear in US movies and shows and honestly makes a lot of Brits cringe.
It sounds like you're literally asking if someone often just writes the words "your parents".
Do you write to your parents often? Should have been accepted, in Duo, do you write "often" to your parents,
does someone know the different meanings of "spesso"? For all i know it means "often" and "thick"
Apparently, it means "often" when used as an adverb, but can mean "thick" or "dense" when used as an adjective. I don't think Duolingo has used it as an adjective yet, so for now it means "often".
They do have used it as an adjective: something about the ice that was spesso, thick.