Thanks for writing all the way from Denmark!
You may want to take a look at Night Owl Remedy for your new kitten. This formula is for animals who are determinedly nocturnal, and whose circadian rhythms are out of sync with the rest of the household. While pursuing behavior modification, this remedy may be great to help retrain animals with the middle-of-the-night crazies and let everyone rest more soundly.
We wish you the best!