OP has stated she is in Australia and it's very hot there. There is a chance her chicks expired from that.
They need fresh water and you teach them to drink by tapping the bowl like a hen would do. If they don't drink, gently dip the tip of the beak in the water so they know what it is.
You can't see water unless it is really gross, so they need clues.
Very young chicks wear out easily and may fall asleep standing up till they fall over.So it is best to have a shallow container of water with some clean pebbles or marbles in it so if the chick lurches forward it will not drown.
Are the chicks eating their feed? Silkies especially may need a finer crumble. Be sure none are bullying the others away from feed and water. If you could show us how you keep them we could offer specific advise.