Children - inferior goods?

Inferior goods are goods whose consumption of or demand for drops with an increase in income levels in the market, other factors remaining unchanged. For instance during the 1990's demand for coarser cereals (a staple food of the poor) had dropped and picked up simultaneously for 'superior' cereals like rice and wheat. This prompted analysts to term 'coarse cereals' as inferior goods. The term 'inferior' does not necessarily mean that the product is inferior in quality. With a sustained campaign that focused on the 'superior' qualities of coarser cereals demand seems to have picked up with the richer people. Anecdotal evidence is available in the form of increasing varieties of ready food products made of coarser cereals which are essentially marketed to the 'better- off' category of people. the data for this needs to be checked though as some might attribute the increased demand and consequent higher prices due to greater demand for cattle feed!
A more interesting debate has been reopened recently with Bryan Caplan in his book " Selfish reasons to have more kids: Why being a great parent is less work and more fun than you think". Caplan argues that the cost of children would be less if parents didn't try to 'overinvest' in children. Such over-investing makes parents less happy and children more expensive according to Caplan. Reducing such investments on children would make them less expensive and hence demand for children should increase (a sort of substitution effect). Betsey Stevenson points out that a fall in price of children would have a substitution and income effect. The income effect as seen by data ( check the Freakanomics site for some interesting data - http://www.freakonomics.com/2011/06/10/the-rich-vs-poor-debate-are-kids-normal-or-inferior-goods/) is negative. People on an average tend to have fewer children as income levels have increased. Such data has to be controlled for other factors such as tastes and preferences to get a 'ceteris paribus', picture. The cross section (across countries) and time series data adjusted for inflation shows a strong negative correlation between per capita income levels and fertility rates (average number of children per woman). Does this mean that there is a substitute that is more preferred to children as incomes increase? Two important explanations for this trend is to be found in a) increasing opportunity costs and b) desire for higher standard of living. With increasing income levels the opportunity cost of having children increases. So there is a clear choice made here. But why not use the increased income levels to hire 'nannies' to take care of your larger number of children while you continue to work. This could reduce the opportunity cost and you could still have fun with more children. But then in a competitive world where demand is not independent parents try to ensure that their children have the best care , education , training etc all of which costs more ( over-investing) . Reduction of such investment is tough when you live in a comparative world where your utility is driven not just by your consumption but by how much you consume more than your neighbour.
More the children less the other comforts such as a nice house or a car etc. It looks like standard of living (as defined by more consumerist benefits) is a clear choice over children as income increases.