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.
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Thames Valley Police named the victims as Savaan Mundae, Jaspal Bahra, Thanh Nguyen and Captain Michael Green.