The disappearances of missing 25-year-old and her two-year-old daughter are being treated as a murder investigation, Police Scotland have said.
A 50-year-old man from Dundee has been arrested and charged in connection with the deaths of Bennylyn Burke and her daughter, Jellica. Police Scotland has not confirmed the specific charge.
Officers are still searching for their bodies.
Police Scotland said the second child reported missing has been traced and is being supported.
Ms Burke and the two children were reported missing from their south Gloucestershire home on Monday March 1, having been last seen on February 17.
The 50-year-old man will appear at Dundee Sheriff Court on Monday.
Detective Superintendent Graeme Mackie, of Police Scotland's Major Investigation Team, said: "We are now treating the disappearances as a murder investigation and I would urge anyone with any information to please come forward and speak to us."
He added: "Bennylyn's next of kin have been updated on the arrest and are being supported by colleagues from Avon and Somerset Police. Our thoughts are with her family and friends at this very difficult time."
Anyone with concerns or information can speak to a local officer or call Police Scotland via 101, quoting incident 1434 of 5 March.