Is it true that pelvic x-rays taken on new born babies may produce cancer in their teen years?

While it may ever. So slightly increase statitical risk (any x-ray does), the chance is infinitesmally small, in the range of being struck by lightning.
NO. No evidence , x rays are taken in new born only if medically indicated , the dose of exposure is so small ( even x ray machine is adjusted to baby size ) and nothing to fear about future cancer.