There are baby change facilities crammed into the accessible for disability toilets because unfortunately, when disabled people campaigned to get these spaces provided, no one realised stores and businesses would do that - short sighted I know.
So there was no requirement that the spaces be protected just for the disabled people who campaigned to have them, stores found parents would use them and so put the baby change facilities in there too, nothing to stop them doing that.
Since parents are a much bigger spending market than disabled people, and parents aren't complaining about it, the disabled people just have to put up with it and be grateful we have what we have, one toilet, for a huge building, even store like Ikea or a huge 24 hour tesco mega store will still only have one, MAYBE two accessible toilets.
The Equality Act when it comes to accessible toilet provision is laughably weak - so many accessible toilets are in fact NOT very accessible at all, the addition of baby change units has meant I can't get my wheelchair AND myself in some of them. Attempts to meet the criteria for accessibility are piss poor and there is next to fuck all anyone of us can do about it when we come across it.
Imagine having to go to the loo with the door open and your chair wedged in it, and outside that door theres a whole supermarket full of people?
Then of course there is the key issue because chances are, its locked with the stores own RADAR key, you can carry your own (I do) but that means if you're in there and someone has the key from the desk, they will assume they can come in. Most stores fit the RADAR locks incorrectly, on purpose. fitting a left hand lock to a right hand door (or vice versa) will allow the locking mechanism to be over-ridden with another key. This easier for stores to maintain rather than fiddling with a coin to emergency access the toilet.
So you have to go ask for the key - like a child asking permission to use the loo, demeaning no? But whether you ask for the key or use your own, you know someone else can just waltz right in.
Know what its like to be bent over the loo having your arse wiped by a carer, or in there by yourself trying to clean up a poo-splosion and some bloke walks in, or some Mum with three toddlers... beyond demeaning. Fucking horrifying. Not just a momentary embarrassment but a 'makes you seriously reconsider ever going out again' type experience.
I am sure that going to the loo when you have a pram and some kids is awkward - but you can plan ahead, you can make adjustments for yourself for a few years - buy a smaller pram, ensure you can shift the valuable items from your pram and leave it outside the cubicle, go shopping with a friend, order online and stay home until you can go out by yourself, go to stores that do have toilets big enough for your pram. Take your kid back to the car, or home, to change them (after all, that is what most disabled people who need to change have to do, as VERY few places provide a Changing Places facility!)
You can tell stores you DON'T like being forced to use facilities provided for disabled people (but I bet you won't bother).