I think trollies being stored together, in the street, under the rain, people put their bags inside, we do not know what kind of hygiene they keep in the warehouse for the items we buy, etc...
Kids are the least of trolly problems. Dont kids wear clothes to cover the diapers anyway?
I feel as grans, it is harder for you to sympathize with moms with young kids and daily activities - are you aware how hard is to go grocery shopping with a child?
It takes 3 or more times longer than normal, the kid wants everything and tears, wants to run to everywhere, little grabby hands, etc.
Ways easier to put the child inside the trolley - honestly.
I bet if a child is running wild with the parent chasing the kid - posters wouldnt be happy and judge the parent too. No win situation
And yes, a stranger comes to me to tell me my child shouldn't be in the trolley, you would be told politely to mind your own business.