How to keep 4 week olds away from the layer food?

[Sunny Side Up]

Flock Raiser is too expen$ive

That's one of the reasons I don't like my adult birds to eat chick starter, because that costs more than the layer feed. Most of my chicks are enclosed in cages or tractors, but there's one open pen where broodies stay with their chicks and another open pen with 4 teenage ducklings. I can't hide the food from the bantams in those pens, and I've given up trying...