We're a family of 5 and it's really difficult to get appropriate accommodation here in Europe. Our children are also just over 2 years apart (now 9, 11 & 13).
This is where we stayed in Rome. We were in one room. Hotel Britannia.
http://www.hotelbritannia.it/eng/index.html
We go to Italy a lot so I have other recommendations if you need them for elsewhere.
We were going to stay here but changed for other reasons. I've since read good reviews of it elsewhere. Base2Stay, London.
http://www.base2stay.com/
I got what they call a "serviced apartment" when my parents came to visit me when I was living in London. They're usually very nice and with a kitchen, it'll save you money on food and eating out, which is terribly expensive in London.
London hotel rooms are tiny so even two rooms wont be enough space for a rollaway.
Connecting rooms is also tricky. The older hotels don't have many or any even. Often, we had to split up, me and the girls in one room with my husband and our son down the hall. Not recommended but if you're desperate...
We have resorted to chains. Novotel is good for accommodating our number of children. Lacks atmosphere but often well located.
http://www.novotel.com/gb/hotel-3269-novotel-london-city-south/index.shtml
We also stayed elsewhere in the U.K. with Premier Inns;
http://www.premierinn.com/en/hotel/LONOLY/london-kensington-olympia?cmp=GLBC
Both of the above have multiple properties in London.
Have only been to S'pore pre-babies and changed planes once in Dublin. Perhaps others can help with those cities.
