During the time the nest had been brought indoors to show the children, a mystery leafhopper appeared on the inside of a window. Anyone who has looked at 'hoppers' closely will know how difficult they can be to identify, often requiring examination of the genitalia to be certain, a fiddly and time consuming operation.
Fortunately this was a fairly distinctive looking specimen being narrowed down to one of three species found on Acer. As Field Maple belongs to this genus it was a good bet that the 'hopper' came in with the nest.
A close look at the face pattern revealed it to be a female Acericerus heydenii a species first identified in the UK on the south coast in 2010, though there is always the possibility that it has been overlooked before.