At what age is it safe to use breathable mesh cot liners? My 10 month old is a very active crawler, so able to get himself in and out of most positions.

Red Nose does not endorse any specific brand name products.
There have been some concerns expressed about the use of mesh bumpers, especially if they are not fitted correctly.

Parents are generally concerned about the potential for injury from the infant bumping up against the cot sides, or getting an arm or leg stuck between the slats.

Mesh type bumpers are unlikely to reduce impact of child hitting sides of the cot, unless they are soft & padded.

Red Nose does not recommend using soft & padded bumpers in the cot.

https://rednose.com.au/article/at-what-age-can-i-introduce-cot-bumpers-and-pillows

United States Consumer Product Safety Commission data has shown that infants suffer essentially no long term injuries from contact with cot slats.

If you do use this product, ensure you follow the manufacturer’s instructions in relation to installation to reduce the risk of entrapment.