Police have been carrying out extensive enquiries to find the missing siblings. Officers say the search has been complicated with the closure of their school. It's thought the youngsters may try to travel by train to a previous holiday destination in Borth in Wales.
Police say they need help from the public to find them. Anyone with any information should contact police on 101.
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Showers continue across some southern and western areas tonight.
Two people are being treated in hospital after an "explosion" in a flat in West Dunbartonshire.
Tom Billings, 22, went missing in Canada in December 2013 during an eight-week trip of North America.