Black stork Must-toonekurg Ciconia nigra
The two bigger storklets are only three days old, one is a day younger which shows too, but all are well and sturdy.
Feeding is easy for the adults at first. Half-digested food which the storks-to-be digest better is regurgitated for the storklets (they already know that food comes from a beak and one must stretch towards there). Larger fish and anything that is not suitable for the storklets the adult eat themselves and so the ”table” gets cleaned up too.
If the fourth egg in the nest has not produced a storklet by Saturday it is plausible that for some reason it was not fertilized.