Look like blues to me, probably mixed with fawn & white. I have three that look basically like yours, and that is what they are from--if so, you can probably expect some yellow ducklings too, as some may have gotten two blue dilution genes, which makes for a pale colored duck. All will have only one black gene, so the blue will be paler than in a true blue (which would be two black genes and one blue dilution). And of course, the partially dominant "runner pattern" gene, which gives you the characteristic white & whatever pattern of some runners would explain the patchy yellow on chest and neck--the ducks would be carrying only one "runner pattern" gene each, so that's why it won't be as regular a pattern.
True blues will often have a pale yellow chest, but it's not usually so distinct as what you have.
So, am I right?
One thing is certain--they are utterly adorable.
P.S. It occurs to me you could get the same genetic result from a black x fawn & white cross, in which case there would be no all-yellow ducklings, because there would be no chance of two blue dilution genes (since the black parent wouldn't have one to contribute). (Edited to add the P.S.)