I do supervise my children adequately, thanks.
"The difference is, that teenagers and bigger children on equipment meant for children of a younger age are probably capable of using more advanced equipment or choosing other games, therefore they are probably mucking about and perhaps shouldn't be there."
Whether they are mucking about, or are capable of using more advanced equipment should have no bearing on anything.
If they are restricted from using some equipment, the only possible justification is that their larger size creates hazards for smaller children.
If they want to use the equipment when it is not in use, the who would complain? Not I, certainly. If 14 year olds want to mess about on the toddler climbing frames, it's no skin off my nose (as long as they don't cover them in jelly) but I expect them to piss off when actual toddlers need them.
Obviously that is not a fair expectation for adults for whom that equipment is devopmentally appropriate, but neither is it reasonable to expect toddlers to be put at risk.
Now, either there is no risk from larger children using the same equipment at the same time, in which case all size restrictions must go, or there is a risk, in which case that risk still exists when you are talking about LD adults.
Clearly many people think anyone of any size should use any equipment as they please without restriction, with no attempt to create places where the smallest can play without constant close supervision (including toddlers with SN).
I prefer that we figure out safe ways to share the resources we have.
It doesn't mean I hate children with SN, or think they are scary, or want my children to be "protected" from feeling "intimidated" by them.
I just want there to be places where smallness is prioritised over bigness without a need for constant parental hovering.