You really should not have attempted breeding since you obviously were not ready for it. Newly hatched bettas are this big - . That's right, the size of that dash. Smaller, sometimes. Microscopic fish need even tinier microscopic foods, which you obviously did not have ahead of time. I don't understand why you would breed when you don't have the needed supplies.
But, like another poster has mentioned, the deed is done. Find some brine shrimp eggs if you can, and hatch them. The bigger fry will be able to eat them, unfortunately the smaller ones will likely starve to death. But, if you were not prepared with food, I'm guessing you aren't prepared to have potentially hundreds of fish either, so it's actually a good thing in your case. If you don't have any live plants in there either, put some in ASAP and turn on a super bright light over the tank and leave it on 24/7 so the microscopic critters can bloom from the plants and the babies will have something to eat.
Egg yolk, I have heard, will work in a pinch but as MrV said, will pollute the water immediately. You will absolutely HAVE to do daily water changes using it, which you have to do anyway after the 2 week mark.
PLEASE, if you ever want to attempt to breed again, be sure you have the money, the time, and the supplies weeks ahead of time. And make sure you do your research, as you would have known all of this if you had.