отвечу сама себе, нашла информацию на сайте финских жд, может кому еще пригодится.Children aged 10 and younger travel free of charge on night trains with a parent in the same sleeping compartment if a berth is not booked for the child. Please note the following matters before departure:• Tell the ticket office clerk that a child will be travelling when purchasing tickets so that a free of charge train ticket may be printed.• Train tickets entitling a child to travel free of charge are available at ticket offices and by contacting VR Customer Care by phone.• If you buy CarTrain packages or your night train tickets from VR Online Shop you may book free of charge tickets for children to the same sleeping compartment at the abovementioned sales points.• Children under the age of 6 do not need train tickets.