Interesting thread...as we are having similar issues all the time (and keep vacationing in the US because its just so much easier with kids in hotels).

Here are a few more tips:

- In Vienna, the Le Meridien is a great hotel and has various Junior-style suites that come with a sofa bed.

- In Greece (if relevant) the Romanos 'single' beds are actually queen size (140cm in width)

- The Sheraton at Frankfurt airport has great family rooms, so does the Sheraton Munich airport

- It always helps asking (we were just confirmed a suite in advance at Schloss Fuschl, but i guess based on status)

- Hotels in Europe do know the issue of US guests arriving and being surprised that 4 people can't stay in the same room, so it is possible to gamble...

Apart from SPG, Novotel is a brand that has designate family rooms with a sofa bed. Not the most luxurious brand, but it works for families.

Good luck !