It's important that you give your co-parent notice and preferably get their express permission in writing if you wish to travel outside the state with your child. If the other parent refuses to cooperate, you can ask for the court's permission in advance.
A consent letter is recommended for all cross-border travel, even for a day trip, if the child will be travelling alone, with only one parent, with friends or relatives or with a youth group.
In California, when there is no court order regarding custody in place, both parents have equal rights to the children. However, California law requires written consent from the other parent before removing minor children from the state, whether for relocation or vacations.
There's no set government form for this, but what you can do is just simply type a letter. It just has those details. Your child's name, when they're traveling, where they're traveling, who they're traveling with. And you just need to sign it, giving their permission to do so. The reason you need this is.
A consent letter is recommended for all cross-border travel, even for a day trip, if the child will be travelling alone, with only one parent, with friends or relatives or with a youth group.
In the USA, though, unless there's a court order requiring permission from both parents, a child may travel (even to overseas) with either parent/guardian without showing proof of permission from the other parent.
Most U.S. airlines will permit children who have reached their fifth birthday to travel unaccompanied. Kids ages 5 through 11 who are flying alone must usually travel pursuant to special “unaccompanied minor” procedures. On some airlines, these procedures are required for unaccompanied children as old as 14.
You should obtain a child travel consent letter granting you permission from the absent parent to leave the country with your child (having it notarized is not required, but highly recommended).