A Coastguard spokeswoman said they were hoping to get in contact with the parents of the two boys.
She said: "We would like to hear from the parents to confirm that the children are, in fact, safe."
It is understood that the boys were reported missing at midday but the parents had not been in contact with the emergency services since about 1pm.
More top news
The huge counter-terrorism effort is placing an unsustainable strain on wider policing service, one of the most senior officers has warned.
A man and woman have been arrested on suspicion of murder after a badly burned body was found in a garden in Southfields, south-west London.
Kim Jong-un has called Donald Trump "deranged" and says he will "pay dearly" for his threats, according to North Korea's state news agency.