See attached images from McDonald’s website.
A 4-piece chicken nugget from McDonald’s has 174kcal, 8.7 grams of fat which is 12% of an ADULT’S daily entire daily need, and 0.38g of salt, which is 6% of an adult’s daily entire need.
A small Happy Meal chips has 237 kcal, 12.1 grams of fat so now a whopping 17% of a full size adult’s daily diet, and 0.44g of salt so now 7%.
So maybe quadruple those percentages for an 18 month old? I don’t know how many chips you’re giving your child; you say a few, but then you say his older brother doesn’t eat any because the younger has them. If the 18 month old is eating them all, no, it’s not good. If he has four chips, yes, it’s probably fine.
And yes, the fries are more atrocious. Of the two, I guess you’d be better off giving him nuggets.
But this is like one of those doctors’ appointments where you discuss something of less import and then in the last 30 seconds mention there’s blood in your wee. Giving both your children diluted squash several times a day is much worse than McDonald’s twice a month. Can you afford the dental work that’s going to cause? If not, stop the squash tomorrow and every time they have a meltdown, look at prices for dental work on your phone. I know it won’t stop the meltdowns, but it will help you stay strong. Not to mention the trauma for them of going through extensive, avoidable dental work. When they’re absolutely screaming the house down in a dentist’s chair, as so many children under the age of 10 do, they won’t be saying, “Oh yes, this is worth it because I so enjoy squash.”