Well, your ducklings are blue with bibs (might be some black but really hard to tell in the light), but not good bibs at all.
Pastels are basically the mallard pattern with two Blue dilution genes. It is the same as what is called Apricot in bantam Mallards. The birds you have got are not close to that at all - they have Extended Black, which means you would not want to use them in a pastel breeding program. They may well carry some of the relevant genes (the blue ones anyway) but the Extended Black will just mask anything that you pair them with. Plus, the bib will keep cropping up.
Unfortunately whoever sold you these did not know much about breeding Pastel Calls