Baby and Toddler Pochos

When searching the site, I found a pattern for a simple baby/toddler ponch where you make two rectangles and sew them together: Here is the patterm:

I was wondering how to know how wide and how long to make the rectangles to fit each individual child. How would you measure a child for this type of garment? Does the child’s head size come into the equation?
Thanks for the help. I am a beginner… but I really want to learn.
Ellie :slight_smile:

Here are some similar patterns. Maybe you can get some sizes off of these.