They only ate the bread
Bread they already accept is doing its job. It lets them sit at the table without hunger becoming the whole story.
The bread counts
Leave the other food on the plate. Tomorrow the bread can be there again, with the same new food beside it.
Eating the bread means they came to the table and ate. That is the part to keep.
Wheat changes this plate
If wheat is an allergy, bread, pasta, and oats stay off. Use the starchy food they can have: rice, potato, or another grain that fits.
Do not swap in a wheat bread to make the meal easier when wheat is saved as an allergy.
Do not retire the other food
The beans or the vegetable can stay on the plate even if only the bread is eaten. Presence is still an offer.
Taking the other food away because they chose bread teaches a very clear lesson. Leave it.
A sentence you can say
“Your bread is here.”