So, I've chosen for my house the Enchanter's Tower instead of the Bedrooms (because, according to the http://www.uesp.net/wiki/Skyrim:Bedrooms, "It is not necessary to build the Child's Beds or Child's Chests (or even the Bedrooms addition at all) in order to adopt children. The Single Beds in the Main Hall are sufficient."). But even after making those mentioned beds (and even the double bed of the entryway), when I approach a child to adopt him, all I can say is that "I have a house, but no room for you".

So, what am I missing? Or is it the wiki mistaken, in such case I'm gonna create a voodoo doll on the one that added that note?

you need 2 childrens beds and 2 childrens chests.

In other words, I better start looking for that voodoo doll, right?

Luckily, I have some saves I made prior creating the beds....I feel pity for the boys, but I really want the Enchanter's Tower (and no, it's not enough having the Enchanting Table in the Main Hall...not for my character).

I could probably look for a mod to fix that, but it's not really worth the time :/

OK, fortunately, no voodoo dolls are required...just the dressers for that room -pfhiu!..-

For the single beds in the main hall, you only need both single beds, and the chest of drawers in between. For the bedroom wing you need the two child's chests as well as the two beds. And it does not matter if you only want to adopt one child, the room has to be furnished for two children.

Edit

Glad you solved it Dovakhan.

Did you make sure that you built both the beds? If you don't you won't be able to adopt any children.

Yep, both beds created, with their drawers. Now I'm able to adopt, thanks.