NO MARGARINE!!! Lots of trans fats!!! Trans fats = BAAAAAAD fats!!!!
(Biology lesson to follow.....)
Basically, ANY hydrogenated fat, even partially, is a bad fat, for kids or for adults. Babies and children need the fats in order to build brains cells and neurons, among other things, and for cell maintenance and growth; fats are incorporated into cell membranes. As you ingest good fats, like flaxseed oil, fish/cod liver oil, coconut oil, butter (saturated, yes, but good fat b/c NOT hydrogenated), and olive oil (OK for boiling pasta and low-temp sauteeing, but not for high-heat cooking as it breaks down into bad fats), as well as nut oil when old enough, the oils become part of a healthy body, improving the growth of myelin along neurons necessary for learning and controlling movement - first large-motor, then fine-motor. Now imagine what happens if instead of good fats, bad ones (hydrogenated, or fats that have broken down due to high temps) are substituted. They are the ones that become part of cell membranes, they are incorporated into myelin, but they don't work as well as good fats. Immunity isn't as good, motor skills don't develop as quickly and aren't maintained as easily. They also take a LOOOONG time to get out of your system! This can also result in emotional and behavioral problems, as I've seen first-hand.
Above and beyond that I'm kinda fuzzy, but since we're so darned diet-conscious here with Josie's sensory issues and her diet, I've learned an awful lot about this stuff in the last few months and I try not to get militant about it but sometimes it is HARD!!!! LOL
In the States, it's becoming more common labelling practice for foods with no trans fats to SAY they have no trans fats, BUT a small amount of them apparently counts as "zero" on the Nutrition Information label. A bag of microwave popcorn is meant to be shared among several people, according to that panel (more than one serving in a bag), so if you eat it all, you WOULD get a significant enough portion to count as a couple grams of trans fat, so even if you read that stuff, it's still good to check the actual list of ingredients.
For cooking, coconut oil is great for high-heat frying. It smells yummy too! I don't normally love coconut, especially not in candy (BLEAH!), but I really do like the smell and taste of it. Yes, it's pricey compared to basic veggie oil, but I don't know at what temperature those oils break down so I just don't bother with them myself except for baking (personal preference). Olive oil is OK for low-temp cooking, but flaxseed oil and fish oil should not be used for cooking, I have been known to mix them with other foods already cooked, though. I do also cook w/butter sometimes, although usually I'll cook veggies and melt a HUGE pat of butter AND add some extra-virgin olive oil to get more good fat. Cringe if you want, but since I started eating that way I lost TWENTY-FIVE POUNDS in 3 months and it has STAYED off!!!!! (Oh, and the kids like it that way too, with a little salt and/or garlic powder added).
OK, my discouse on fats is ended now. Thanks for indulging me!