I remember only one short part of the movie:

A teenage boy is brought to a cell in a prison (or something similar). Could be his first night there. He's lying on bed in prison. He's obviously anxious, sucking his thumb one time. He falls asleep and dreams of being a little boy, peeing. In reality he wets the bed, the wet sheets are shown.

Can anyone help?

The origin could be russian or something, but absolutly not sure. Movie seems to be older.