Re: How will Clark being found by the Kents be handled?
The Martha's sister's child thing is among the least believable explanations in my opinion. In the real world, taking custody of a family member's child involves legal documents and proceedings and the child would already be in the system and have things like a birth certificate. The whole ruse would collapse as soon as anyone discovered that there are no records of the sister giving birth. Clark needs those sort of documents if he is ever to get a driver's licence or attend college.
I think simpler is better. Have the Kents claim they found the child abandoned and have them get legal custody through the system. Smallville is a small community and everyone would know about the difficulties they have had trying to had children of their own, so I'm sure the local public officials would speed up the process and make sure it went in their favour.