We have tried telling her we are the children and are grown and she sometimes understands. Sometimes gets angry, but either way within minutes is back to worrying about them. We have tried saying they are okay and will be back soon. If she wants them home, calls me repeatedly looking for them. How do we handle this?
The person who is physically with your mother in her home is best placed to divert her. It is time-consuming and frustrating; but the aim is to go with her thought process and reassure her that way, so that you can then get her focused on something else.
So, for example, she demands to know where John and Jane can be. She's very worried that they aren't home by now.
Depending on where she thinks they are - playing with friends, at school, out in the yard - the idea is to go with her belief and find acceptable reasons for their not being home yet. They're staying over at their friends' house. They have after school activities on Thursdays. Maybe they went with auntie/uncle (that's one of you, by the way) to get an ice cream.
Once you have temporarily stopped her worrying, that is the moment to get out the photo album and gently lead her back to the present day if you can; or to a completely different activity which takes her attention away from her children, like lunch, or washing her hair, or visitors.
Who is living with your mother?