TrojanHorse

If you also have Hilton points, I would suggest using Marriott for Sydney and Hilton for Cairns. In the end that is what we did, and then paid for 6 nights at the Courtyard in Surfer's Paradise (on a rate which included parking and breakfast for C$125). My kids were younger than yours are now when we went to Australia. If I ask them today where in the world they want to go - they would both answer back to Australia. They absolutely LOVED it, especially the week in Cairns.

I find Marriott quasi-useless for family stays in Spain, Italy and to a slightly lesser extent France. However, another suggestion would be Marriott in London and the ADT Hilton in Paris. We have done that before, and will be again this summer. Also, the Marriotts outside of London are mostly on pointsavers this summer, so some are 40,000 points for 5 nights (breakfast in but no lounge). I think that is a good value, especially since Hiltons in the same area are 30,000 points per night.