Sure if you just got them yesterday there is no doubt that the little one not eating yet is still a bit stressed. Shipping, and even just switching location, and cages can stress them a bit. One day is not long at all, but at that age you want to let them get settled as fast as possible. That's good you are holding off on the handling for now. Keep on trying to feed him, and give him time to get settled, and adjusted. Maybe you can ask the breeder you purchased from the way he had the cages set up, the times he fed, and what he fed, and try to match the routine the babies are use too.
The size is not grossly small. Babies from different lines, and parents grow differently. If there is a large difference among the babies you received, and they are the same age then there is reason to be a bit concerned. If their all around the same size give or take an inch that's not so bad.. My babies grew a bit faster, but these you received are still young and many factors come into play with growth. They may be just hitting growth spurts a bit later.
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