I've observed as they grow older mom will let them venture further and will also let them "test the waters" before she jumps in. This time of year the fawns are frequently the first to my feeder or food plot and mom will appear some minutes later if all seems quiet. It's getting close to the time when she will leave them anyway, so they will probably be fine even if something has happened to her. They (the twins) may stay together for another year, though.