Grandchildren based in Australia will be visiting their father in UK at Xmas. Communication between father/mother (e-mail only) is bitter following divorce but boy (13 yrs) wants to stay in U.K. with his father for good with this visit. Girl (11 yrs) does not want to visit scared she can't go back to Australia. They both travel on valid U.K. passports. Where do the children stand in the event of their father not allowing them to return to Australia in January. Thank you for your help.