Thames Valley Police said it is "determined" to end a siege at a house in Oxfordshire "as soon as possible".
Local Policing Area commander Superintendent Christian Bunt said:
It is believed the man is armed, although no indication has been given that he wishes to harm the children.
We are doing all we can and our officers are determined to bring this situation to a close as soon as is possible.
More top news
Search teams were again looking for missing airman Corrie McKeague - this time joined by cadaver dogs trained to seek out human remains.
Donald Trump has dismissed pictures showing a smaller turnout to his inauguration compared to Barack Obama's in 2009.
Severe storms have ripped through the southern American state of Georgia leaving at least 11 dead and thousands without power.