Canada
You just file for custody at the courthouse and then go to court. You have to serve the other parent with papers, but that's about it. If there's a reason you can't have custody, or it's been taken away, you need to prove that you've made an effort to change. (Parenting courses etc.) Otherwise, they decide based on what's in the child's best interests. Generally, the first court appearance is brief, they'll assign a court trial date, which you have to go to at another time. Get a lawyer if you can.
United States
If the mother has custody already he must prove to the court that she is unfit.
The factors used to determine that a parent is unfit are generally governed by state laws with child endangerment being the determining factor. The following include some of the reasons a parent may be declared unfit:
Can i get custody of two children i have cared for since their mother 1 yr ago children are not related to me
Yes, depending on the circumstances. Generally, the parent who has custody must be deemed unfit for the court to remove the children from their custody. You should seek advice from an attorney who specializes in custody issues in the jurisdiction where the children reside.
The non-custodial parent can go to court and request custody of the children. A judge will decide which parent should be awarded custody of the children. The circumstances under which the children are currently living, combined with the reason(s) they are not living with you will be a big factor in whether or not you get to keep custody of the children.
She already has custody of her children.
The father was awarded custody of his children.
It depends on the state, usually the state takes the children into custody, or the closest family relative.
You can get sole custody of your children from a previous relationship by by filing custody paperwork through the courts. A judge will then review the case and determine which parent should receive custody.
Joint custody with both ex-wives.
Guardianship, not custody
The word "custody" is usually used in relation to safekeeping or responsibility over someone. An example of a sentence using the word "custody" is "In a surprising decision, the judge granted custody of the children to their father. "
You have the visitation rights that were established in the divorce, and you have no custody rights.
If they do not have custody of the children, they cannot. If they have custody, they can apply to a court for a name change.