The two chicks facing to the front are males with lighter lines
The outer 2 females have the darker eyeliner near the corner of their eyes.
The 2 in the middle are males.
It is possible to sex a Welsummer at day-old because the chicks are marked like a partridge, with a stripe on the top of the head. The stripe is darker on the female so the difference can be seen by comparison. After four to six weeks there is no doubt, as the comb of the male becomes obvious first.