They are hard to open due to a vacuum seal. So just take a very small flathead screwdriver and put it under the lid, and apply a small amount of upward force to break the seal. The jar pops, releases the pressure, and now a toddler can open it. I use the nail file on my pocket Leatherman. Works every time.
Won't you bend the lid and lose the ability to reseal it properly though?
Stick the tip of a spoon under the lip of the lid and push the handle towards the jar. That should open a little gap that releases the pressure inside the jar and it'll open pretty easily then.
One day I will get a consciousness transfer into a fancy robot girl body and then I will open all the jars.
All these people are complaining about how hard it is to open a jar, and I'm sitting here scratching my head because the only times I've ever struggled with jars was after someone closed them too tightly. Just don't use a death-grip when you're closing your jars and you'll be fine unless you're elderly or something.