As a first time mom, I used to get a little nervous when I used to see little babies out and about with their parents with adorably cute helmets on their heads, they looked so cute, but you knew they were wearing them because they had to correct a flattened head situation caused by a soft head and constantly laying their heads on a flat surface for long periods of time. Naturally, I wanted to avoid this for my daughter if possible.
My little girl is now 15.5 months old and enjoying her favorite word, "no"... She's come a long way from tummy time and sitting still! She's now our little destroyer / baby terrorizer as we like to call her since she's at the stage now where she loves throwing things and destroying block castles...
There was a time when she used to sleep in a co-sleeper (which I preferred immensely over a bassinet especially as a first time mom). The first 5 months of her life, my daughter would sleep quite a bit on and off during the day and night and usually stay in the same position, she was spending a lot of time with the back of her head against the sleeper's mattress. I did notice the back of her head becoming slightly flat, and then began trying to get her to sleep with her head to the side, which she eventually did, but then that one side also became slightly flat (she would always revert to the same side). My baby's head was much softer when she was tiny so when she was around 1.5 months old, I started placing a flat head pillow under her head and it made a big difference! Her head was protected from the flat surface so the slight flatness was corrected!
You can find different flat head pillows online but I decided to hand make my daughter's pillow from organic cotton and washable, eco friendly and non allergenic 100% recycled polyester. I made my own since I enjoy designing and making things and didn't want a pillow that was too "puffy" where it could be uncomfortable for her neck so I designed this pillow special for a small head in a small sleeper (some of them online were very wide). She took to it very quickly and slept very comfortably. As a first time mom, I was paranoid about just leaving the pillow floating around in her sleeper since people always warn you NEVER to leave stuffed animals in a sleeper with your baby as it can be a suffocation hazard, so I placed it in a piece of mind way so it was efficient and safe (image bellow).
I used this pillow for the first 5 months of my daughter's life as she wasn't rolling over just yet, as soon as she started rolling over (and was put into her crib), I removed it just to be on the safe side, but by that time her head was nice and round and much harder so I assumed less likely to flatten. Fast forward to today and her head is nice and round! :)