The game the boys are playing, which is translated
as 'dice' the Greeks called 'knucklebones' (astragaloi).
Knucklebones did not have the cubed shape of modern dice, but had an irregular
shape, which can be viewed in the image below of a vase used for pouring
(turned on its side) in the form of a knucklebone.
The Oxford Classical Dictionary says that
"the four long faces of the knucklebones were of different shape, one flat,
one irregular, one concave, and one convex, and in dicing these had the
value respectively of 1, 6, 3, 4." The pouring vessel is decorated
on its flat side with an image of Eros ('Love'), with whom games of chance
were associated.