Feel their crop in the morning and see how it is. If it is still just as big and has that balloon feeling, then it could very well be sour crop. When I treated mine for sour crop, I held food for 24 hours and only gave them water. I put Apple Cider Vinegar in their water. This helps to stop the yeast from growing in the crop. I use the organic one called Braggs. It has the "Mother" in which is what you want.
It will be hard to not give them food for that long and I did give in and give food earlier for mine and I had to start all over again the next day. So just do the water and the ACV for the first 24 hours. I also massaged the crop several times a day to help get things moving and out of there. After the 24 hours and if the crop feels more like an empty crop start by giving them yogurt. This helps put the good bacteria back into their GI system. If all goes well, you can then progress to the chick feed and see how that goes.
Let us know how the little ones are doing in the morning!!! I hope it was just a full crop!!! If it feels empty tomorrow morning, then you don't need to do all of this for a sour crop.