Safety Issues
Theoretically all of the above are allowed on Freegle Groups; the general feeling on Freegle UK Central is to leave the decision on whether to take a seat/mattress/crash helmet or not to the member who wants it, so leaving the members to decide on whether or not they wish to take the possible risks. However, many of these issues are emotive. If you have strong feelings about the use of any of these items you can chose to not to allow them on your group. You may wish to consider polling your members first.
Also, by limiting the things that are allowed for safety reasons we can be, by implication, suggesting that all other things are safe. Once you start doing that where do you stop?
Tip: one solution is to add a 'mod edit' to posts when you catch them in pending, pointing out the risks of using seconding hand car seats and cot mattresses.
You might want to send out the following links, or add them to your links page to refer people to: List Bullet icon http://www.dirtbikerider.co.uk/website_content/how_to/ride/safely_crash_helmet
List Bullet icon http://www.brake.org.uk/index.php?p=489
List Bullet icon http://www.childcarseats.org.uk/
List Bullet icon http://www.nhtsa.dot.gov/people/injury/childps/childrestraints/reuse/
(link to safety admins here)