When can a toddler start sleeping with a blanket in their cot (how old can they be?

Soft bedding is dangerous in a cot and should not be used.
Soft bedding includes pillows, quilts, doonas, soft toys and bumpers.
Soft bedding may cover the baby’s face and obstruct breathing and/or cause overheating.
Older babies in a cot can be at an increased risk of a sleeping accident by using pillows and bumpers as a step to climb up and fall out of the cot.
It is safer to wait until the child starts to sleep in a bed before introducing a pillow or other soft bedding.
https://rednose.org.au/article/at-what-age-can-i-introduce-cot-bumpers-and-pillows
Soft bedding includes blankets