Delayed parenthood: old eggs are around 1% more likely to result in childhood cancers (more or less, at least sometimes, per some swedes). A bit controversial although it seems fairly common sense. Obviously a 45 year old woman's eggs will have been exposed to three times the radiation as a 15 year old girl's eggs, and given that I'm surprised the net childhood cancer risk was so low. From the original paper, which I'm probably misinterpreting, if the kid lives to age 5, there's no further measurable effect, so either the cancer kills them young or it has no effect, and I have no common sense explanation for that...

Fewer children: Seems fairly well proven across many papers that time spent pregnant equals lower ovarian cancer risk. This does not appear controversial. Then again time spent pregnant does seem to increase pregnancy related mortality (duh) so not entirely sure its a net positive.

No idea at all about the last claim. Probably something lactation hormone related. I don't think mere calcium loss is a legit anti-cancer treatment.

Those who have a pregnancy before 20 years of age versus those who have a pregnancy after 35 years of age show a 50% reduction in their risk of breast cancer.

http://www.cancer.gov/cancertopics/pdq/prevention/breast/hea...