If you purchased WDW resorts, it is likely you have deeds that state you both own the property as husband and wife, or similar language, which means you have what is called a tenancy by the entirety, a form of joint tenancy. That means if one you dies, the survivor automatically gets full ownership without going through probate. (Note that avoiding probate does not avoid any estate tax matters, i.e., if taxes are owed they must be paid but with current laws that prohibit any taxes unless the dying person's estate is in the millions, paying taxes is not an issue for many, although you still may need to file an estate tax form to show that the estate owes no taxes. It is when the survivor dies that the probate issue will arise and you will have to go through probate in Florida in relation to the timeshare even though the deceased resided in a different state. The property will be distributed according that last-to-die parent's will, or if no will, according to Florida intestate rules, which would usually mean the one child if the surviving parent has only one child.
To add the child to the ownership requires the preparation and filing with the applicable government agency in Florida, a new deed for each contract you own. Thus, there will be preparation and filing costs for each new deed and any necessary other papers needed for filing. The deed would reflect a transfer from the existing owners to the same existing owners plus the new designated owner. The new deed cannot be tenancy by the entirety because that applies only to married couples. Thus, the new deed would need to reflect that the transfer is being made to joint tenants with right of survivorship. That would mean that the death of one automatically puts ownership into the other two, and the death of the second person puts ownership into the lone survivor. No probate would be needed until the lone survivor dies. Suggested above is doing the deeds and transfer yourself to avoid other than the filing costs. I view that as a possibility done with fair warning -- if the deed is not properly drafted to contain exactly what it must contain, the result can be a future with someone spending much higher costs to try to change the disaster created into what it was supposed to be.
A second method for ultimately transferring ownership to the last survivor requires a three-step process. You don't add the child to the ownership. Instead you create what is called a living trust. The trust is the designated owner of the property and names the current married owners as the trustees and if one of them dies, the survivor becomes the trustee. Those trustees are also the beneficiaries of the trust but you can also make the child a beneficiary who could become the sole trustee and beneficiary when both parents die. Basically the trust would lay out who actually gets what and what role when someone dies. As such trusts usually control ownership and distribution of most property of value, real or personal, owned by the trustees, Also created (step two) is usually fairly short wills which mainly assures that property that might have been overlooked when creating the trust goes to the trust and distributed according to the trust terms.
Once the trust and wills are created, the current DVC owners would provide transfer by deed of their interests in the DVC property, and probably other property such as their home, to the trust. A main benefit of the trust as the owner is that probate is forever avoided because the trust itself, the legal owner of the property, always survives regardless of the death of any of the trustees or beneficiaries.
Of course, having a trust created and deed transfers made generally requires hiring a lawyer and has far more costs than just doing deed transfers, but it does create the avoidance of probate (but not tax matters) for many things someone owns.
