Derek Mitchell, 55, a married man of Cardiff, South Glamorgan, preyed on the boys, aged between 3 and 10, for up to 5 years, Cardiff Crown Court was told. He also carried out a string of rapes on a girl from when she was 10 and raped one of her friends who was 13.
Mitchell was convicted of 20 counts of indecent assault, rape and serious sexual assault committed over a 20-year period.
Passing sentence, Judge Martin Stephens said the crimes were a horrific breach of trust and only a substantial jail term was appropriate. The 14 life sentences are to run concurrently.
During a trial in December, Peter Jacobs, for the prosecution, said Mitchell systematically indecently assaulted and had sex with the boys. He carried out the assaults in his bedroom and each boy was abused in the presence of the others.
Mitchell threatened to give one youngster a "good hiding" if he ever told anyone what was happening and the boys maintained their silence until June last year.
Social services were alerted when a friend became concerned at the "rude games" being played by the boys.
In a separate trial in November, Mitchell was convicted of a string of rapes against a girl from the age of 10. He also molested the girl's brother.Reuse content