I am honestly quite honestly taken aback about the "comments" about Kate staying with her parents following the birth of her baby. Amazed quite actually.
I have never given birth to a child, just a mother by way of life. But for all of my friends who have given birth and/or adopted a child, it was quite natural for their mother to spend some time with them to help them adjust to life with a new baby. As most of these women have "retired" they actually had some time on their hands. One of my friend's mother and mother in law, actually took turns! One stayed one week, the other stayed the next week, etc. it went on for a month.
In addition to helping the new parents with the newborn, they did light housework, cooked the meals, watched the baby when the other spouse went back to work and the mom needed a power nap, and most importantly stayed with the newborn while the parent did things you don't think mean a big deal.
My best friend, said the first time she took a shower after her mom left she brought the baby in the bathroom (they have one of those huge houses and thus huge bathroom), so she could take a quick 1 minute shower to rinse off. The baby was on the other side of the bathroom so that the fog wouldn't affect him but the point was she was scared to leave him alone for a second. When her mother was there it wasn't even an issue. Especially since William only had two weeks of leave.
Maybe this is not the norm for some, so they think this is a bit "immature"? I don't know.