The RNLI says the man and boy were were swept out to sea off Aberffraw, on the west coast of Anglesey.
The man was able to make his way back to shore, but the child is still missing.
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The man and woman found dead on Cardiff's Queen Street have been named as Lee Simmons and Zoe Morgan.
The man and woman who were found dead this morning on a Cardiff street were stabbed. Warning: Graphic content.