P&C spaces are a courtesy, they are not law, they aren't disabled spaces. Just u der half of all adults in the UK are parents, almost half the customers of that store would likely have children with them. In contrast, less then five percent of drivers have a disabled badge. Parking in a discretionary P&C space is not comparable to parking in a Disabled space.
There would never be enough P&C spaces available for every parent. And of those that are available, who "should" use them?
A mother with two toddlers who is popping in for some treats and a browse in the clothing Isle?
A mother with a baby, who is popping in to meet her sister for a quick lunch in the supermarket cafe?
A divorced Father who is going to take his six year old to get some new shoes before handing the child over to their mother in the carpark?
Two parents who go shopping with their baby, the Mother realises she needs to pick something up from a shop at the other end of the High Street, so she goes back to her car and leaves her child with their father as it's easier to go alone than take the child out of the store again?
A mother who is looking after a young child, emergency child care for her sister, both agree to meet at the retail park as it's half way between both houses?
A Mother, who is waiting in the car alone, while her husband takes their child to get some new clothes?
When you see an adult alone in a car that is parked in a P&C space, you have no idea what the situation is. You should keep your nose out of other people's business.
OP, those spaces are just there out of politeness, you can park there whenever you want. Being a parent is a choice, being disabled isn't.