[Glyn Thomas]

how will I found out What sex my 7 chicks they are 3 weeks old

[ANHBUC]

Hello Glyn and welcome to the site.   

There are a few different methods of sexing chicks, some breeds can be sexed at day old due to their markings or colouring (sexlinked).  There is also a method called vent sexing which is specialised and should not be attempted by a novice as it can damage the chick.   Most people who have not bred sexlinked breeds have to wait until they are older and the comb and wattle start to develop and go red earlier in cockerels.  It is not an exact science so it does catch you out sometimes.

If you post some pictures of your chicks and tell us what breed they are someone might be able to give you some idea.