We are in Canberra too, and day trip down to the snow a couple of times a year. We have already done one trip this winter.

As stated, your three options are really Mt Selwyn, Perisher or Thredbo.

They are all about the same distance from Canberra, however we've not ever gone to Mt Selwyn. Purely for the fact that we enjoy having the convenience of Jindabyne close by (20mins from both Thredbo and Perisher; you have to pass through it to get to either, and the road forks off. Left to Thredbo, right to Perisher). Jindabyne has coffee shops, cafes, a great bakery, takeaways and a nice big Woolies.

We usually grab gear in Cooma on the way through from one of the 24hr hire places. There is a slightly cheaper hire place behind maccas, but last year its return time was 9pm. So if you'll definitely be passing back through Cooma before that time, go there, but if there's any chance you'll be running late don't, as there will be no one there to return your gear to!

A toboggan costs about $6-$8 to hire for 24hrs.

Yes, there is no tobogganing allowed at Thredbo (very silly, in my opinion), however you can keep driving about 5mins past Thredbo and go toboganning at Dead Horse Gap, which has a fantastic slope and is much more fun than the tobogganing area at Perisher. My husband and brother (21) had a riproaring time on that slope last year, spending nearly two hours on it, as you can walk about 100m up the mountain and launch down it (or just toboggan at the bottom if that suits you better). You also then have the convenience of having lunch etc. in Thredbo. It depends what sort of toboggan experience you are after and how old your kidlets are

Perisher is very family friendly and has a large toboggan area catering for kids and adults, but be aware it gets PACKED during weekends/school hols, and then becomes a bit dangerous. Once you're moving, there's really no stopping if someone's wandering toddler blunders through your path. During busy periods there are adults and kids absolutely everywhere, it's very dangerous. Perisher is also very expensive for food and again, very difficult to buy anything during peak periods as the lines are enormous, and there is no seating. However going there during the week is really fantastic, and will be perfect for littlies. You can also hire when you get there.

Hope that helps, happy to talk more about my experiences if anyone likes