I've found voice sexing is effective you'd have to wait until they were at least 4 weeks, females will start to have voice changes sounding like.honks boys will peep.longer until around 7 weeks (not all fall into this category each duck has its own timing this is just in general.terms). you could try vent sexing but I don't.really recommend it because you can really really hurt the duckling if you do the slightest thing wrong, there would.be.tutorials on.you tube.they look.about a week old am I right? sorry for all the periods my phone likes them