I am old enough to remember women being criticized for having careers outside of raising a family. That they were being selfish, preferring working over caring for their children. Women who were able to quit working to raising their children were praised as being better than those who worked.
Now women are being criticized as slackers because they put raising their children over a career.
Catherine will be dealing with a 2 year old and a newborn/infant in 2015. I see nothing wrong with giving her some slack on public duties. While many complain that she is not out and about cutting ribbons on this and that 7 days a week, her primary duty is to ensure the Windsor line continues... Giving birth to heirs. So she likes being a mom. I would think many would praise her for her devotion to her child, soon to be children. The alternative would be the Queen's method of raising children, joining your husband in Malta for months while leaving your child behind in London with nannies.
I also seem to recall criticism that she did did not get pregnant sooner.
Catherine just can not seem to please people no matter what she does.