FFS - it's a shit lunch and I'd judge too.
There is no way it's a one off - you don't go from providing perfectly healthy and acceptable lunches to that level of crapness in one foul swoop. You don't think "shit I've run out of bread - I know, I'll send little Johnny with last nights left over takeaway" you cobble something together - crackers, pasta, rice with peas and sweetcorn.
Worst comes to the worst, you go and knock the neighbours door and see if they can lend you a couple of slices of bread or drop the kid off at nursery, go to the shops and then drop their lunch off afterwards.
Don't get me wrong - my kids eat their fair share of junk / sweets / chocolate but sending a child that young to nursery with that lunch is indicative of a more ingrained piss poor attitude to child nutrition or a massive lack of knowledge on the subject, both of which need to be addressed.
People minding their own business, being scared to judge and raise concerns, trying to find excuses for shit parental because no one wants to say it is shit - these are all reasons why the obesity rates are now at over 25% by year six. They are the reasons why tragedies like Daniel Pelka occur. They are the reasons society and community are breaking down.
Sometimes, it is ok to judge, sometimes it's OK to call people on crappy parenting or raise issues with the relevant professionals. Sometimes it is OK to hold people to certain standards without worrying that they might be depressed / the child may only want to eat cold greasy chips / it is the third Thursday of the month and therefore feed your kid shit day.