Yes but you can choose your connection when you book the flight! I've done this several times, so have my parents en route to Sydney.

(If you were travelling with an 8 and 10 year old would you do a short or longer stopover?
Any tips?)

Personally, I would stay a few days in Singapore if you've not been before - it's quite expensive (but about the same as Sydney!). Your kids the right age for Universal Studios, Sentosa is great and there's a good water park (Wid Wild Wet) also the zoo is one of the best - can thoroughly recommend Night Safari. If you're carrying loads of luggage can leave in left luggage downstairs. Taxis are really cheap and MRT great. China Town worth a visit too.

I fly long hual a lot with work (Perth-Dubai-Entebbe-DRC) and can say that Singapore is a great place to change. However, do have a think about breaking the journey and staying in Singapore for a couple of days. It can be done very cheaply. We did it through singapore airlines and they offer a fantastic deal that is effectivly subsidised hotels. We paid $20 for a couple of days in the Singapore Ritz and it includes tickets for attractions and return transfers.
I would also consider not travelling BA/ Qauntas. I avoid them like the plague as i find their service just isnt up to standardn and far better airlines can offer deals just as good.