Significant life events, such as having more children, should be included in an update of a will, but if not the impact varies from state to state.
In Georgia the will gets revoked, according to the Wills, Trusts & Estates Prof Blog in "State Law on After-born Children Leads to Revocation of a Will."
In a recent court case, a Georgia man created a will in 1989. He later had three children out-of-wedlock, but he never updated his will to include the children. The Georgia court decided that the will was, therefore, invalid and revoked it.
The man's estate would thus be distributed according to the state's laws of intestacy, as if the will never existed at all.
Every state treats these after-born children (who are not mentioned in wills) differently.
An experienced estate planning attorney can advise you on creating a will that fits your unique circumstances, according to the laws of your state of residence, as well as updating your will as needed.
Reference: Wills, Trusts & Estates Prof Blog (Oct. 17, 2017) "State Law on After-born Children Leads to Revocation of a Will."