Two mice is fine if your snake will eat them both. If not, try 2 smaller sized mice or large hoppers.
I typically start my hatchlings on multiple rodents per feeding after about 4 weeks. I prefer to feed single or multiple smaller sized prey items to all of my ball pythons (no matter what age) as opposed to a single large item. I feel this helps them to become more consistent feeders.
Hope this helps.
-adam
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