I'll try and help with what I can as I am working with Hong Kong students...but all I can say is good luck!
Start be pre-teaching the vocabulary though questions. For example, say "hello, my name is ..." and then get one of the students to say this with you. Or pre-teach the language through written questions, exercises. Everything has to be topic related and have a purpose.
Hopefully, pre-teaching the language verbally for about 30-40 minutes should get them to use the language for the last 20 mins, but if it doesn't, then ensure that they answer written questions or statements about the language topic that is being taught so that when they come to practise the language at the end, they can refer to their notes for help.
Whether they are 4 years old, or 17 years old, you have to look at the country your in (Sweden in this case) and really find out what the age groups like in their social life.
Not to be rude or dismissive towards your teaching activities, but sometimes (and it has been in my case too) the age group which you teach may not find the games you introduce to them fun enough to become involved with. Students like to tell you through their body language that they will do the work, but it's really boring, and they just never get focused into the lesson.
You may need to speak to the parents to discuss the difficulty you're having and get them to help you give an insight into what their kids like at home, in school, outside of school time. You basically have to research their way of life and adapt your course material to be meaningful AND fun to them.
I've got some 4 year olds who like to sing and tell me what they've drawn in English, I've got the 8-14 year old boys who like to talk about battle spirits (a card game...which I still don't understand but appears helpful when getting them to speak in English)....and then the 8-14 year old girls vary dramatically from not talking, to playing hangman, to playing dictation games, to playing pictionary, and some who don't want to learn speaking through games but through written exercises and poetry.
The point is, tailor your lesson to the age group, and in my case, to the individuals and the class. Once you get to know the students, you'll be able to work around them using the language.
And finally, if you really believe that all avenues have been tried, just smile, give them a piece of paper, and go through a conversational scenario with them, giving them the step by step lines of what to say when (for example) you are shopping. This is not creative, nor does it get them to think much about what they are saying, but they at least do hold a general conversation for a minute or two, which I feel is very encouraging when all other avenues have been tried and tested.
At least you're getting one word answers. Be grateful you are not getting the students who reply to my "Good morning Class!" with "I want to die!"