I know it can be unpleasant to get an extra charge, but this is very standard for Europe. What I like about this hotel is that it has good air conditioning and is close to many metro lines, so although it may not be your best deal ever, you should be fine there. It sounds like the amount of the charge has still not been resolved. Looking at lemeridien.com, the hotel's cheapest website rate is 329 Euros during this time, but a room with two double beds is 374 Euros, so from that point of view you got a huge discount off the website rate. If you want to resolve this now, you could telephone the hotel and ask for the cost to be upgraded to a room with two double beds, or you could ask the cost of a rollaway. However, in the room we had, I'm not sure a rollaway would have fit. If you don't resolve it, take a sleeping bag or an air mattress for your child and hope for the best when you check in discreetly.