It certainly looks like a Welsh Harlequin- As far as sex goes- Hearing the voice would give an indication. I have colouring like that in my Harlequin Runners - but can be either male or female. It can depend greatly on the strain and bloodlines of the WH. Some males have a very dark head and the females much lighter - but with some strains they are very similar at this age. I would guess as a female from what I can see in the photo- but seeing it standing up to see the tail area and breast would also help to decipher by colour what you have.