A colourful form of motivation to train motor skills of the hands, too!
4 different shapes and colours.

Castanets are percussion instrument used in Moorish, Ottoman, ancient Roman, Italian, Spanish, Portuguese and Latin American music. The instrument consists of a pair of concave shells joined on one edge by string. These are held in the hand and used to produce clicks for rhythmic accents or a ripping or rattling sound consisting of a rapid series of clicks. They are traditionally made of hardwood.

In practice a player usually uses two pairs of castanets. One pair is held in each hand, with the string hooked over the thumb and the castanets resting on the palm with the fingers bent over to support the other side. Each pair will make a sound of a slightly different pitch. The higher pair, known as hembra (female), is usually held in the right hand, with the larger macho (male) pair held in the left.

The origins of the instrument are not known. The practice of clicking hand-held sticks together to accompany dancing is ancient, and was practised by both the Greeks and the Egyptians. In more modern times, the bones and spoons used in Minstrel show and jug band music can also be considered forms of the castanet.

During the baroque period, castanets are featured prominently in dances. 

Köçek troupe at 1720 celebration fair at Sultan Ahmed's sons' circumcision.

In the late Ottoman empire, köçeks not only danced but played percussion instruments, especially a type of castanet known as the çarpare, which in later times were replaced by metal cymbals.

(from Wikipedia)