I have followed this thread with interest for several reasons.
It's been many years since I have had the delight / issues of having DC in prams/ buggies........... and I cannot remember specifics on how we "coped" with my / our toilet needs, just that we did. When they were young I used a sling most of the time do guess I just "went" with that in place ! There were not that many "disabled" toilets around either 
These days I know (and work with / support ) far more people with disabilities than I know with young DC so see the issue from that angle more. I know how hard it can be sometimes to locate an accessible loo.... and just how necessary they are ..... there most definately are far, far more toilets available to "mums / parents and babes" without accessability problems.
I can however also see the point that, statistically speaking, at any one time there may be more people with buggies around than people in a wheelchair .... so maybe a wheelchair accessible toilet may be "free" for a greater amount of time. Not sure that is a valid reason to use it though if one does not need the facility ! A service provided for a mum to BF may be vacant most of the time but non bf people do not go in for a sit down ???
I liked carrots thread reitterating that we dont know for sure the issues affecting even the people that are "able bodied" and that no one should judge by the appearance of the person coming out whether they are "entitled" to use the facility or not.
On a good day I can work normally, I can push wheelchairs etc and walk long distances.
On a bad day I can be on crutches and / or I can get desires so intense to urinate/ defecate that I cannot move a step without "leaking". To make it to the nearest loo can be painstaking and if the disabled loo is the nearest , even by a few metres then that is where I go. ( might also need the extra facilities in that loo) When I come out ( with whatever expression an observer defines) sometimes the expression might be absolute
if I have not made it in time and I know I smell .... or it might be huge relief . Whichever it is I hope no one has hoisted judgeypants and questions me 9even if I have my newest DGC in a buggy with me
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as I hope not have to relate my medical history to justify my use of a loo. .......
Would also like to say that there are of course disgraceful incidents / misuses... like queues of people with buggies outside accessible loos for convenience rather than need and flipping eck people not taking buggies out of wheelchair spaces on buses ...... but a lot of the time its about confusion as to the defnition of the space. The label on the door can be defined differently by different people.
However in my local A**a store....... get this
one door with wheelchair logo
one door with female logo and a crutches logo
one door with a male logo and a crutches logo
one door with a baby change logo
( the female loo I know has an ickle toilet and two full sized )
all logos also in braille
...so they seem to cater for everyone /every interpretation ...... unless YOu know different !