They have a limited life span for safety reasons and can be hard to on-sell, so some 200,000 end up in landfill every year.

But those that are donated to family members or friends and used beyond the recommended 10 years are also troublesome.

"Old, worn or damaged seats can suffer reduced structural integrity," Kidsafe president Craig Ray said on Wednesday.

"Materials degrade over time and through repeated use and seats become less able to protect a child in an accident."

The federal government is hoping to make disposing of seats and protecting children's safety an easier task for parents with a $20 million investment in the product stewardship program.

It was successfully trialled in Queensland, NSW and Victoria in 2017.

Old seats can be used to make outdoor furniture, flooring, bollards, garden edging, retaining walls, posts and stakes.

Environment Minister Sussan Ley has signed a memorandum of understanding with car seat manufacturers, retailers and motoring associations to adopt a seat care program that makes it easy to dispose of old and potentially dangerous child safety seats for recycling.

She's also added the seats to the priority list for legislative framework that manages the environmental, health and safety impacts of products.

Australian Associated Press