In testing for the Hip 2 B Square Tee, we found that a few people didn't like having a seam right under the armpit. Most were ok with it though - especially after adding the step to clip the corners of the seam allowance to reduce bulk.
If your child has sensory aversions, you may wish to lower the top color block seam. Here is how you would do it:
Simply add on 1/2" (1.25cm) to the bottom of piece F1 (as shown above), and remove 1/2" from the top of the F3/F4 (for fully color blocked option) or F2 (for partially color blocked option) pieces.
Alternatively, you could remove the 1/2" from the top of the bottom piece (F5) instead, if you want more length on the center panel.
Then just cut and sew as per normal!