We are taking a guess that the handlebar on this bicycle are intended to be a long arm rest, as used on some triathlon bikes. It is one 'handlebar' only, so it sits flat on your sleeve, reducing the chance of catching on things.
Also, the seat appears to be very high, so we don't envy any little cyclists who would like to try to ride these - particularly as the wheels don't spin. However, on your sleeve they will certainly do the job.
Dimensions (LxWxH): 27mm x 18mm x 5mm (approx.)
Weight per cufflink: approx. 5.02g (light)
Size = x mm (W x H)