I have suggested that infant baptism is an act of the parents signing the contract before God to raise their child as a Christian.
Just as the parents can, on their own authority, enroll their small child into some club or open a savings account for him, they can incorporate him into the Church, as well.
The responsibility then is split between the parents making every effort to impart the faith into the child and the child learning well.
Suppose then that both fail: the parents fall away from the Church or neglect their duties, and the kid grows up into something other than a Christian.
In such a case, I think we have an invalid baptism, a breach of contract, or even fraud before the Almighty. The baptism was literally a meaningless ritual. If I were in this situation as a 14-year-old, yet “found religion” at 24, I might want to be re-baptized.
We might say that multiple generations are united into a one body of Christ and one Church through the family and household on the foundation of natural love. If this chain is broken, infant baptism is ineffective.
(Against this opinion it may be argued thus: if a baptized person becomes a Christian at any point in his life, even long after the age of 14, then his baptism is immediately validated, and the parents’ neglect is irrelevant. If he never becomes a Christian, then his baptism was in fact invalid or at best futile, but it would have been invalid even if the parents had done their best; so the parental solicitude again is irrelevant. In this sense confirmation is indeed baptism consummated.)
However, the sign is made as much before men as before God, and since no outsider can monitor the inner life of a family, a priest can never claim that some baptism had no force.
If Smith was baptized as a child, then given away to a non-Christian family at an early age, does not even know he was baptized, and yet again chooses Christianity later in life, then second baptism again is lawful, though this time simply because it is inevitable due to ignorance.