We always put really finely grated carrot in our rissoles too. They can also be made with leftover cooked roast. Sooooo yummy on a slice of bread with tomato sauce.
On the jumper thing. Jumper (or windcheater) is what you would call a sweater, what you yanks would call a jumper we call a tunic (or maybe sometimes a pinnifore). They are really common winter uniform for primary school kids. High schoolers more often wear a skirt in the same material.
Tunic
And while we are speaking of that. Schooling varies over Australia but in general.
Primary school is Prep (or reception depending on your location) to year 6. I think our prep (prepatory year) is what you call Kindergarten, then we have years 1 to 6.
High school is year 7 to 12, in year 11 and 12 you do your VCE/HSC/final exams to get your mark to go to Uni.
When the housemates so 'that is so year 6' they are saying how primary school/tweenie it is, since most kids are 11 or 12 in year 6.