I'm sure Middleton had a nice quiet birthday because for New Year's Eve she went out to party and drink with her sister. William was not with them. Not very royal of her, especially as a new mother. Middleton the so-called "royal" left a baby at home so she could go drink - not so impressive. Locals said that she was "very jolly", meaning "drunk". I'll bet a few people at the palace said "put a lid on her" and they toned things down for her birthday. Middleton was always fond of drinking, and that's just from all the "had too much" photos of her that were taken over the years.