Sexing for these 5 week old chicks

[Fourboysandchicks]

These chicks are Orpington x olive egger (I believe) they were hatched at our school. Any ideas on sex? The other 2 are silkies. (These I might have to wait awhile to sex). Thank you for your help!

 

[Tookie]

The silkies are to young for gender, I'm not good at silkies anyway. I think the other two are both cockerels.