From the 1880's until today, model steam engines are very popular toys, and not only for kids. In the late 19th century, model steam engine manufacturers such as Bing introduced two types of miniature steam engines: mobile (boats and locomotives) and stationary steam engines. Later, fire engines, steam rollers, wagons & traction engines began to appear. Around the mid 20th century, there were many toy firms producing toy steam engines.
Doll, Krauss Mohr, Carette, Falk, Doll, Marklin, Bing, Schoenner & Plank were the biggest firms manufacturing steam engines around Nuremburg. Smaller companies were Eberl, Bischoff, Hess, Issmayer, Scholler, and Neumeyer. In France, Radiguet and Rossignol were two major manufacturers of toy steam models. UK: Bowman, Mamod, Burnac, and USA: Empire, Jensen, Weeden and Ind-X.
What's it worth? Take a look at this Model Steam Engine price guide: sold listings for a value indication.