In Luxemburg there exist (existed) two miniature railways:
Luxemburg the Vallée de la Petrusse, situated between the Pulvermühl railway viaduct and the Pont Viaduct there was a narrow gauge railway line. It was created in 2004 because of a garden exposition in the park. It was in exploited by volunteers. Children (and their parents) could freely make a ride when the railway was opened. This was for years the case on Sunday afternoons.
Unfortunately we have to talk in the past. There was a need for a parking place. In 2020 the city government of Luxemburg took a part of the place where the rails were situated and transformed it into a parking area. There are plans to make a new location in another park in the city of Luxemburg, plans are that it will be opened in 2023. But nothing is sure in this case.
A nice video of the last day of the exploitation on 25-5-2020 can be found on rtl.lu.
In the north of the city of Esch (in Lallange) there exists a miniature railway with 184 mm track width. It was created in 1997. Children and adults can make a ride with this train for which two lines exist, one of about 1000 meters, and another of about 350 meters long. It runs on Sunday afternoon in summer period. There is a steam loc, two diesel locs and a motor wagon and further several coaches. The line can be found just near the terrain of the football club US Esch.
More info can be found on Rail.lu