I'd like to try the AED but as I said, they don't actually have one
They didn't actually touch upon infant injuries at all. We spent about an hour on child injuries, but as the instructor said, that's a huge minefield because children are A) drama queens, B) surrounded by their overprotective parents, and C) if they're alone, it's a massive can of worms lawsuit-wise. But, with CPR you have to use your own judgement. You won't be compressing as hard as you would on an adult, but you still have to do it hard to make sure it actually takes effect. Similarly though, as long as you act in accordance with first aid rules, you are legally safe from being sued/arrested, as long as you can prove you acted in a reasonable manner. For example, if somebody has a spinal injury and is on their back, but there's a good chance they may vomit and choke, you can put them in the recovery position. Doing so has a huge risk of paralyzing them for life, but NOT doing it can lead to them dying. It's dealer's choice which one you do, but you aren't held accountable for it.
Another thing they touched on with CPR is dealing with the elderly. You have to do it hard, obviously. But the elderly are far more frail than adults are, and where CPR will probably just bruise an adult's chest/ribs, chest compressions on an 80-year-old run a pretty high risk of breaking bones. However again, it's based on preservation of life being the highest priority. A broken rib is better than dead.
The problem with taking someone to the hospital without real medical help if they're having a seizure or a cardiac arrest, is that you just don't have the ability to care for them while taking them there. First-aiders are exempt from certain rules, but putting someone going through cardiac arrest in a car is a horrible idea. It's just not safe, so in cases like that it is best to wait for paramedics, even if they do take a long time to get there. Hence the 6% survival chance.