Are you using crumble or pellets? Mine don't like pellets that much and I feed them crumble. It seems a bit easier, especially for ones that are still pretty young, to eat.
Like Den in Penn said, they will eat them and won't starve themselves. If you're having a problem spilling the food, try putting it on a block of wood, or some bricks. That way they can still reach it, but not scratch around in it.
Another thing you can try is mixing in treats. Put small dabs of plain yogurt, blueberries, cut grapes, bits of oatmeal, and they will try that. My chickens go crazy for those treats and sometimes to get them to try something new, I just mix the new food, or the food they "don't like" with something I know they like.
Chickens are kind of like children sometimes when it comes to trying new foods. Some determine they don't like it, even though they never tried it! You just have to be persistent and it will pay off.