The Bantams will probably be up a tree when dusk comes.
Do they have a coop, or do they sleep outside?
It's just one of the drawbacks with free range chickens.
If you leave food out for them permanently take it up. What I did mainly so I could do a head count was hand feed them something nice (small pieces of cheese, walnuts and grapes work well) towards dusk wherever I found them. Day by day I moved closer to where I wanted them. Eventually they got used to treat time at the final location and tended to be there waiting at dusk. The Bantams still went up a tree but at least I knew where they were and could start getting them used to the idea that a coop at night wasn't such a bad idea.