Do you have the parents on premises or did you order the eggs? If you know for a fact that the parents are split charcoal your whites can be charcoals just covered by the white. If memory serves me you would get 25% charcoal 50%IB and 25% plit charcoal chicks from a split pair. The only way to know for sure is to wait til they breed. If the whites end up hens and do not lay any eggs then they are charcoal white hens. If they do lay fertile eggs then they are IB split to charcoal whites. Now if the whites are males and you breed him to a plit to charcoal hen and you get 50% charcoal and 50% plit then it is a white charcoal male. Knowing the exact background on white chicks is the key to knowing what they will produce unless you are going to just breed them with another white then all chicks will be white.
Charcoal hens do not lay eggs, but there have been breeders saying that spalding charcoal hens lay eggs but I have never seen anyone post about it or if they were fertile or not.