I'm curious, would the sentence still have the same meaning without the word "agar" in it?
It should also be accepted to have "Mother says that....."
Definitely. In many other sentences in this course only the literal translation, which in this case is "says", is accepted.
Can "agar" be replaced with "akan" or "kepada" in this context?
no, the synonyms of "agar" is "supaya". if you wanna use "kepada" in this context, you can make the sentence : ibu berkata "kepada" kami "untuk/supaya/agar" berhati-hati.......
Wouldn't a better English translation then be:
"Mother says, that we should be careful when driving this car."
tells us... = says to us to be careful... ?
So what exactly does reduplication do?