Newly hatched ball pythons are given hoppers and quickly outgrow them. It's a real hair puller in the BP world that unknowledgeable people will tell new owners to feed their youngster fuzzies or hoppers when they SHOULD be on small adult mice at least.
The rule of thumb is to give the snake a prey item about as big around as they are at their widest body point. If weight of the prey can be known, then give them something 10% of their own weight.