At breakfast, a toast of whole wheat bread could be offered as a source of carbohydrates, for example, with natural tomato. Other options such as industrial pastries, although quicker and more accessible, are high in sugars and unhealthy fats.
To add healthy fats, you can put olive oil on toast or spread a little avocado.
You can also have a dairy product, such as milk (whole or semi-skimmed), yogurt (unsweetened or unsweetened) or, for example, add a little cheese on toast.
Juice, even if it is natural, should be avoided. It is always better to offer the piece of fresh fruit and let them take it in bites. It will even be more attractive if pieces of fruit of different colors are mixed.
What they did not have for breakfast, will be a good idea for lunch.