When is it safe to introduce a pillow to a toddler for sleeping.

Red Nose recommends that you withhold a pillow from baby until they are at least 2years old & no longer in a cot.
https://rednose.org.au/article/can-baby-use-a-pillow-to-prevent-flat-head
https://rednose.org.au/article/at-what-age-can-i-introduce-cot-bumpers-and-pillows