You might have a restriction on how far from home you are allowed to take a foster child; conversely, you might be able to take a child out of the country for a vacation.
Even if you know that you are allowed to travel out-of-state in order to visit relatives, you'll have to inform the fostering agency of your plans.
All travel, must have the written authorization of your agency and/or county social worker. Parents are required to inform their social worker of the whereabouts of the children at all times, including if there are plans to travel.