Thanks to everyone for the outpouring of kindness to me.
By “undoing” a baptism I meant either removing the record of the occurence administratively, or some other way of making it ineffectual (like Peter was told in Mark 16:19 KJV - And I will give unto thee the keys of the kingdom of heaven: and whatsoever thou shalt bind on earth shall be bound in heaven: and whatsoever thou shalt loose on earth shall be loosed in heaven.) Does the catholic Church believe they have the authority to loose something in heaven, especially when something wasn’t done in a kosher manner?

I know full well that the past cannot be changed.
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Thanks all and God bless.
Gazelam:
As a former LDS, I may be able to bring a bit of insight into what you’re asking, and explain to the Catholics here why you are asking this.
In the LDS religion, the fourth article of faith states, “We believe that the first principles and ordinances of the gospel are first, Faith in the lord Jesus Christ, second, repentance, third, baptism by immersion for the remission of sins, fourth, laying on of hands for the gift of the Holy Ghost.” (Not sure how old you are, but I was singing the song in my head from Primary that helped me memorize that and helped me to get a little button on my Merrie Miss banner.)
To be put on the records as a member of the LDS church, all four of these things must occur, under the authority of a holder of the LDS priesthood. During baptism, any sins that occurred before this time were washed away according to LDS teachings. Also, while going through the washing and anointing ceremonies, which are a precursor to the endowment ceremonies in the LDS church, there was a phrase in the ceremony that basically said I was “clean every whit”, amounting to a second baptism, which I found very comforting at the time.
When I decided to leave the LDS church, I had to write a formal letter to the LDS church headquarters in Salt Lake City, which removed me from the membership rolls of the church and in effect “unbaptized” me and took away my temple blessings (from being endowed). In essence, leaving the Mormon church for good involves and administrative process. Were I to revert back to the LDS church, I would need to be rebaptized to fully join the church and reconfirmed.
In traditional Christianity (Catholicism), the baptism is a supernatural ceremony which in essence replaced the circumcision ceremonies of the Jewish tradition. As the Jewish circumcision ceremony represented a permanent mark on the child to represent the sign of the covenant between God and Man, so too does the sacrament of baptism leave a permanent “mark” or change of state on the soul of Man that represents the new covenant of God and Man after the sacrifice of Christ.
In addition to the “mark”, the apostles taught that the baptism was a supernatural form of the natural purification rites of the Jews, which were a type in the Old Testament leading to the true purification of being washed free of sin by the blood of Christ on the cross.
Looking at baptism in this light, it should be a bit clearer on why the Catholic/Christian sacrament of baptism is looked upon differently than the baptism of the LDS church. While the LDS church does see the rite of baptism as an initiation into the LDS church, the Catholic/Christian tradition sees baptism as an intrinsic transformation of soul and a mark of a covenant between God and Man. Because of the transformational properties of the Catholic/Christian baptism, this cannot be reversed in any way.
Even when faced with excommunication from the Catholic church (which is a much more complicated affair than LDS excommunication), excommunicants remain Catholic because of baptism and are still obligated to attend Mass. However, they are no longer able to receive any sacraments except for the Sacrament of Penance (confession). To have the excommunication lifted does not require a rebaptism, but instead an absolution from the proper ecclesiastical authority. Excommunication is very similar to disfellowship in the LDS church, in that there are still obligations required, but very little options for benefits from God through the authority of the church.
On a related note, when I converted from Mormonism to Catholicism, I was baptized at the Catholic church after a series of classes for adults similar (but a bit more involved) than the missionary classes of the LDS church. The Catholic church does not consider the Mormon baptism a valid baptism due to the fact that while the baptism is said in a Trinitarian form, the intent behind the words does not baptize in the name of the traditional Christian Trinitarian view of God. Because of the nature of God is drastically different in the LDS church than in the Catholic church, the intent is considered invalid. Had I come from a protestant church such as Baptist or Presbyterian, I would not have to be rebaptized. The Catholic church recognizes any baptism done in the name of the Father and the Son and the Holy Spirit as recognized in the Trinitarian view of God.
Also, the sacrament of baptism is the only sacrament that can be performed by a lay person in an emergency situation (dying baby, etc.), as long as there is the proper form (I baptize you in the name of the Father, and of the Son, and of the Holy Ghost) and with the proper material (water). If your wife had decided to give your son an emergency conditional baptism in her home, as long as she said the proper form, and had the proper intent, and used the proper material, the mark would at that point be on the soul of your son and the effect would be valid.
It does sound like your family is in a very painful struggle. You and your wife and child will be in my prayers.