Whereas there are kids who will insist, on catching a glimpse of my dulcimer, that I have brought along a guitar there is no mistaking the triangle. And while 'kokiriko' is a name that is rarely remembered, 'triangle' is never forgotten.
Triangles have been used in European orchestral music since the 18th century. Like any instrument it is difficult to play well, in spite of its simple appearance. It is now used in popular music, too, and is very much a part of the Latin percussion collection. Good quality instruments are made of carbon steel but school instruments tend to be made of stainless steel. Probably the finest triangle I have ever come across was made of hammered brass. It was at one of Michael Deason Barrow's Tonalis workshops and was just one of a truly wonderful collection of instruments.
In orchestral situations tone is everything and the triangle must be suspended by a piece of string to prevent damping. To stop the instrument from spinning when hit with the beater, this piece of string needs to be an inch or so long (2.4cm). Tying a short length of string between the handles of a large bulldog clip will provide a secure mounting for the triangle as well as a way of holding the instrument. The clip can be held in the hand or attached to a stand. A metal beater is used to strike the side opposite the open corner.
The application in Latin music is much more rhythmic, the tone being secondary. A larger triangle is used and it is suspended over the index finger of the hand you don't write with. This hand is used to allow or damp the sound as required by the rhythm being played by the other hand. Damping is achieved by simply gripping the instrument with the rest of the holding hand; this has the effect of stopping the metal from vibrating.
Children are frequently underwhelmed when presented with instrument, looking wistfully at whatever has been given to their peers on either side. However, a quick demonstration of the damping technique will give them something to think about. They should master Pattern A without too much trouble. If you really want to impress them, master Pattern B and play it at speed. My own triangle seems to have been confused with a school collection so, for the time being at least, you must make do with the dots. When I either reclaim or replace the missing instrument I will post an audio demo.
As it is not a great expense you might like to buy a variety of sizes. An 8" instrument will cost you less than than £5 (pounds sterling) and a 4" less than £3.