If you have a child who is born or adopted after you create your Will or Trust and you have not provided for them in your Will or Trust, then the child is considered an "omitted child".
An example: You create a Will on January 1, 2018 that states that all of your assets will be left to your parents. On December 1, 2025 your partner gives birth to your son, James. Unless you update your Will accordingly, James is considered an omitted child.
An omitted child is entitled to a "statutory share" of your estate. California Probate Code Section 21620 states:
Except as provided in Section 21621, if a decedent fails to provide in a testamentary instrument for a child of decedent born or adopted after the execution of all of the decedent’s testamentary instruments, the omitted child shall receive a share in the decedent’s estate equal in value to that which the child would have received if the decedent had died without having executed any testamentary instrument.
The "statutory share" is what your child would've received if you died "intestate", i.e., without any estate planning documents. This amount will depend on whether you have a spouse and how many children you have at the time of your death.
There are exceptions to the "omitted child" rule, and they are specified in California Probate Code Section 21621:
A child shall not receive a share of the estate under Section 21620 if any of the following is established:
(a) The decedent’s failure to provide for the child in the decedent’s testamentary instruments was intentional and that intention appears from the testamentary instruments.
(b) The decedent had one or more children and devised or otherwise directed the disposition of substantially all the estate to the other parent of the omitted child.
(c) The decedent provided for the child by transfer outside of the estate passing by the decedent’s testamentary instruments and the intention that the transfer be in lieu of a provision in said instruments is show by statements of the decedent or from the amount of the transfer or by other evidence.
California Probate Code Section 21622 also provides a couple of exceptions to the general rule:
If, at the time of the execution of all of decedent’s testamentary instruments effective at the time of decedent’s death, the decedent failed to provide for a living child solely because the decedent believed the child to be dead or was unaware of the birth of the child, the child shall receive a share in the estate equal in value to that which the child would have received if the decedent had died without having executed any testamentary instruments.
Thus, if you were under the mistaken belief that your child was dead (but was not actually dead) or if you weren't aware of a child you had, he or she would be entitled to a statutory share as well.
It's a good idea to include a provision in your Will or Trust that describes the members of your family to avoid future problems. Additionally, if children are born after you execute your Will or Trust, it's good practice to review your estate planning documents and have them updated.