You can feed a baby ball rats, just sometimes mice are easier as they have a different smell. Though the best thing to do is to go for rats off the start or switch to rats ASAP because this can be a problem when they get larger and one mouse per time doesn't cut it, then it'll cause them to grow slower.

I will always recommend f/t over live because if your snake hits that mouse/rat wrong and that mouse/rat takes a chunk out of your snake it can cause issues that would of been easily avoided by feeding f/t. Your snake can get a bad infection or that can seriously cause a BP to go off feeding and tons of other things. So it's honestly best to do f/t though not always the most convenient for breeders and what not. I brought some f/t feeders to a girl and I watched her feed her king snake a weanling rat and because it didn't get the head just right I saw that rat take a chunk out. It's cheaper to go with f/t over live in the long run unless you breed your own.

The black pastel I have when I got him had only eaten one meal a hopper mouse, I fed it f/t rat pink for it's next meal and it's been on rats since, so whoever told you that is quite wrong.