I think is just a snack left for them. There are two of these with the parent feeding the Ko, one with a pet family and one with a gutter trash family.
...Requesting a translation for this and the other one I mentioned.
It's just a piece of chocolate on top of a biscuit (cookie). Mother Reimu does comment on how luxurious a meal it is, though, as well as the obligatory "Super Cooking Time!"