The junk food was in honour of the fact my eight-year-old was having a friend to play and I figured that the usual afternoon tea of whatever healthy items remained in her lunchbox wasn't going to cut it. But the whole scenario just underscored the universal truth that we seem to hover in some perpetual state of quasi-guilt about almost every aspect of parenting.
It's no doubt amplified by the sheer overload of information - the endless research, the studies, the articles and the websites - about wrangling children.
Just after my daughter was born I wandered towards the parenting section of a bookshop, idly in the market for an uplifting read that related to my new role in life.
The first sentence in the first book I picked up said something like: "You're a new parent so you'll be feeling confused, tired and a little uncertain."
I dropped this book like a hot potato. I wasn't feeling any of those things.
In fact, if I really stopped to analyse it I might have been feeling the complete opposite. I'd been lucky in all sorts of ways.
I'd had an uncomplicated emergency c-section, a pain-free recovery and had plenty of support.
Most of all, I was grateful to have a gorgeous baby after two miscarriages. I'd never felt more blessed.
I certainly didn't need some patronising textbook to tell me all the negative feelings I was supposed to be experiencing.
And right there was the first dose of potential guilt.
Was I actually meant to feel guilty for not feeling the way that most new parents allegedly do?
It was a case of once-bitten, twice-shy and I avoided one-size-fits-all advice from then on, instead turning to experts - such as medical professionals, teachers and speech therapists - for bespoke input when the need arose.
The whole notion of perfect parenting is surely unhelpful. In what other area of our lives are we urged to strive for perfection?
In our relationships, jobs and sporting endeavours we're encouraged simply to do the best we can. Yet for some reason this isn't the prevailing approach once you take on the role of mother or father.
Of course the parental guidance industry has a vested interest in making us feel inadequate and in need of supplementary advice. The books, the television programmes, the parenting courses are all designed to first inspire then assuage our guilt.
It's a shame there's been no concerted effort to communicate the core reality of parenting - that most of us are far from perfect.
We're just doing the best we can, what suits our circumstances and keeping our fingers crossed that it'll turn out all right in the end.
It's a truth that was shared between us two mothers in the dairy that day as we supported the junk-food manufacturers.
Beneath the protestations and laughter was an acknowledgement: We're not even close to being perfect parents and we're okay with that.
