I moved to Sydney from London this year with similar aged kids and also for 2 years. I would echo everyone else and say a relocation agent can be helpful - think through your answers to Surfsup questions and they can help you start planning while you are still in UK.
Our experience has generally been positive, we live in North Shore which is a really easy commute to CBD (15 minutes door to door!) as we decided it was just too far getting to the Northern beaches. Schools are great around here, lots of playgrounds, beaches near enough although you have to drive and can pop into the city as well. I think further out would have felt just a bit too suburban for me.
Things we have struggled with is mainly the cost of living. I was told that you should times your UK £ salary by 2.5 and this is the amount in dollars that will give you roughly equivalent lifestyle and we have found this to be the case. My husband earns a high salary, but I still find myself shocked by a cucumber being sold for $4, tennis lessons after school at $250 for a 10 week term and babysitting - we pay an agency fee and then $22 an hour on top of that. Ditto cleaners far more expensive. I'm not sure professional salaries, esp in finance and law are that much higher over here btw.
I found renting our home quite emotionally difficult, had just done an extension and spent a fortune on Farrow and ball paints and was sad to leave a couple of months later for someone else to enjoy/make marks all over. I would also budget for times when the house isn't rented, we had a difficult first month with no one in the house and had to bring the price down a lot to get a rental. Prices in central Sydney are similar to London if not more expensive, my dreams of pool and sea view never materialised!
Finally I found the move quite hard as a trailing spouse. Great your husband is on board, but has he worked out what he will do day to day? I find it difficult, husband goes off to challenging new job, kids settled into school well which is great, but they get to go off and have new experiences. I think lots of trailing spouses feel a bit left out as they just get to potter about at home and try and make new friends.
We've generally had a great experience, I like the fact the kids have learnt about life in another country and have a much more global perspective. We made the right decision, but I do feel I left a lot behind and we won't be paying off the mortgage living over here. I think you need to work out if you want a family adventure, or if this will advance your career or have another good reason for the move. Otherwise there will be days when the kids miss home or you do and it's good to be able to reassure yourself that the move was made for a good reason.
Good luck
PS Specifics, holidays suck here and husband only gets 20 days (down from 28) which is a shame. Also check if your salary includes 'super' which is the pension payment everyone has to make here - you get it back when you leave, but will take 9% off your salary each month.