Magna Aura

Four children travel through Christian's grandfather Ronson's tower and with blue light that develops at a thunderstorm over 1,000 years to the past. They discover the supposed-sunken city Magna Aura and meet there Drago who looks similar like Christian's grandfather, his brother Morton who rules Magna Aura, and three children who become their friends. In the present, Ronson, his son-in-law Alexander, Elena, the mother of one time-travel kid, and two other children try to get back the kids.