When disqualifying trans fat, are we qualifying cis-fat as healthy?
If cis is what's naturally found, by default it's unsaturated fat isn't it? 


Both cis and trans are unsaturated.  "Unsaturated" means having at least one C-C bond that is not a single bond (but instead a double or triple bond).  The terms cis and trans refer to the geometry of the molecule about the double bond.   

Trans fat also occurs naturally in milk, for example fats of vaccenic acid

Also, since a fatty acid can have more than one double bond, it can be both cis and trans, for example fats of Rumenic acid found in milk. 




  When disqualifying trans fat, are we qualifying cis-fat as healthy?


Cis-fat can also have negative health consequences.  For example, according to the review article Dietary fat, insulin sensitivity and the metabolic syndrome Clinical Nutrition vol. 23 pages 447-456.


  monounsaturated and ω-6 polyunsaturated fatty acids have less negative effect on insulin sensitivity than saturated fat


In other words, even consumption of too much unsaturated, naturally occuring, cis fat can have negative health consequences, such as insulin resistance.

Your question says:


  Because everything they adore seems to contain trans-fat from breakfast cereals, syrups, chips...


but is this really true? 



From what I've seen, cereals have little or no fat of any kind, let alone trans-fat.  

Similarly, maple syrup has no fat.  



Even potato chips don't necessarily contain any trans fat:




  So we gotta explain why they should go for trans fat free, unsaturated food or in the worst case just choose a saturated food instead of a trans-fatty thing


The amounts of partially hydrogenated trans fat in foods has been greatly reduced in the last 10 years.  Milk and meats naturally contain trans fat.  

I wouldn't want you telling my kids they can't drink milk or eat a hamburger.  Sure it's bad to eat too many hamburgers.  The focus should be a balanced diet.