When Superman’s human parents first encountered Superman at the crash site, he was an infant. It can be inferred from the comics that Superman is able to eat human food normally even though this would contradict how his biology is depicted as using solar power only. However, Martha and Jonathan Kent should not have known this fact since there was no information on Superman’s race available to them. Furthermore, they are somehow able to guide him through infancy and childhood despite the lack of basic knowledge about his species.
Is there a canonical explanation for how Jonathan and Martha Kent could have acquired the knowledge at the time they found him?