Gizzy said:
LGB have in the past released battery powered versions of the Spremberger steam engine, and the KoF diesel loco.
In fact, the Spremberger is currently available as a rather brightly coloured item for the childrens' market;
http://www.lgb.com/en/products/narrow_gauge/details.html?page=&perpage=10&level1=6218&level2=6229&art_nr=90200&era=0&gaugechoice=36&groupchoice=98&subgroupchoice=0&backlink=%2Fwww.lgb.com%2Fen%2Fproducts%2Fnarrow_gauge%2Fsets.html
I guess it could easily be resprayed black or dark green, and made to look less toy like....
Aieee, the dreaded "Harlequin" loco!

Actually as Gizzy says, with a repaint it would be quite acceptable - though I have read that its infra-red control system (as opposed to Playmobil's radio unit) is not very good, and almost useless outdoors.....
The (now very old) original battery versions of the KoF and the Kleine Dicke/Spremberger had a manual control lever on the side (forward-off-reverse, single-speed), which could be activated by a post clipped onto the trackside to provide a primitive "shuttle" control so that the loco could run backwards and forwards on an end-to-end track as well as running round a loop. The locos were very basic indeed, with all-plastic wheels and minimal coupling rods, virtually no separate details (no handrails etc, and no lights), and ran on two big D cell dry batteries in series inside the bodyshell, giving a massive 3 volts....
The size of the batteries provided both a decent run-time and the ballast weight for the loco!
You can still find these old locos around on evilBay now and then, though ones in pristine condition are quite collectable - but a slightly tatty one can be had quite cheaply and could be very handy for small visitors to play with.
Jon.