Intelligence is hardly a factor in the context of raising a child. Someone who scores very low on any number of intelligence tests may well be a great parent. In fact, (in the US) people of higher intelligence are less likely to produce offspring; if they do, they are more likely to produce fewer offspring than parents of average or low intelligence. This is not a counter to your claim, but it does suggest that most intelligent people are potentially unlikely to produce offspring at all (and this is actually a common case).
I understand that when you use the word intelligence, you may be referring to some level of ability not related to taking tests. In that case, a better word than intelligence could be used, perhaps?