Totally understand it can be difficult especially with young kids but as one poster has mentioned above there needs to be some degree of prioritisation that you decide. How will people working longer hours in the shops on Sunday get their downtime with their kids or do their hobbies/other commitments.
We do manage as I've said. I was trying to give a balanced view against those frothing at the mouth at the evil people advocating extended hours

As you've said, there would be a small number of people that would need to work extra hours, but there are already many people doing so in the same supermarkets and elsewhere in the supply chain. Where do they get their downtime? Why are we protecting a handful of till staff and not their colleagues?
Not in retail, but I've worked in a 24x7 environment for 15 years and in that time period have worked shifts and done call out. We didn't moan that we needed to work weekends because hours can be planned around. My wife and I in a situation at the moment now both kids are at school full time where we're trying to develop ourselves for the good of the family to ensure that we can provide the very best for all of our futures. It means that midweek time is precious.
As for small shops, I did mean local independents stores rather than the small express branches of the large supermarkets. Sunday trading laws do infact help to support them quite a lot. My in-laws have a shop and finding staff it a nightmare on Sundays so they then do put in the long hours themselves but it keeps the business afloat.
I suppose a lot of that would be down to locality. Almost every independent near me has closed, yet I could just about throw a stone at two mini Tesco stores and a co-op. The first Tesco is open 5am til midnight, the second is 6am til 11pm, the co-op is 7am til 11pm. No-one is protecting those retail staff.