The standard Taijiquan, Xingyi and Bagua zhang instructions tell us to lift up our heads from the Baihui point on the very top of the head. Some Shaolin and meditation schools say to lift from a point a little further back so that the chin comes in slightly. Further, I have heard lift from the roof of the mouth, lift from the base of the skull and even lift from a point in the air about one foot above your head.
All of these instructions are useful gates. It is vitally important to develop awareness of head position, centerline, dingjin (upward power), and zhengqi (upright, self-correcting vigor). However, I think these instructions alone will not produce a high quality final product.
I've now spent way too much time looking at baby pictures on google images, I may need some time to recover my manliness. Unfortunately I could not find a single picture of a monkey swing so I'll have to describe it. Here is how you do a Monkey SwingTM:
While sitting down place the baby on its back in your lap with the its feet facing you. Take hold of an ankle and a wrist in each of your hands. Then lift up and swing the baby's bottom toward your face and then it's head out and away, using your forearms as the pivot. Continue swinging until the desired results are achieved.
As you are imaging this, you might think that the baby's head would flop backwards like that of the child on the swing above. But it didn't. The baby's head stayed right in line with its torso. This was a five month old I was watching, a younger baby probably would have had a floppy head. An older child would certainly be able to do this, but in most cases it would be obvious that they were using voluntary neck muscles.
The baby I watched did all this automatically. Her head was inside her dantian!
The highest level martial artists put their head inside their dantian.
A baby development site.