I agree with a previous poster here in that iOS ain't always as simple as it seems. Here's my story I will try to keep it short. To bypass my long winded story just head down to pros and cons.
Firstly for initial use and learning, iPad is very good. Where it gets complicated for them (my mom and dad now have iPads but struggle with things like app store, how to close multiple running apps, how to do any basic trouble shooting etc) is the app store process. Basically get used to the fact that you will always have to help them out with tech regardless of what you buy them.
Remembering passwords for apple ID, wifi, router connecting etc, regardless of what platform you buy. Explaining why you have to put in your visa info when you aren't actually PURCHASING an app etc (although I don't completely understand that myself when its a free app), explaining the app updating process etc, when you should or shouldn't update the device to the next OS, regardless of platform etc etc etc.
Pros and Cons:
In favour of iPad:
If their needs are really that simple than you should be able to dodge the beast that is known as itunes. But you will have to help them set up the device and don't even try to explain iCloud
.
Battery life is compared to NONE. And my go to device is my tab S. I have an iPad mini and have owned iPads, and battery is a HUGE deal. So iPad shines here.
Initial monkey push button and get banana results works great with iPad. (after you set up all of the email accounts etc) which you would have to do with either platform.
Apple care with one on one etc is worth it's weight for seniors I find. Peace of mind and easy means of remedying any problems. It is also less expensive than Best Buy protection plan.
Also a good resale value if it doesn't work.
Cons: iTunes, explaining iCloud.
Android tablets:
Android is not so complicated, it has the same set up process as iPad etc.
Basically anytime you have to get a senior to jump into any app settings is like throwing a kitten into a starving dog cage. It ain't pretty, thats what a good son/daughter is there for.
The cost of a tablet can be fairly less than an iPad especially if you are not sure of your investment being received well.
Extra and cheap storage for an android tablet is nice.
Different E-readers available which can convert any type of file extension is nice if you could ever convince them to read on it. Again for both device types you would have to lead the way.
Cons: battery life and explaining anything about how to adjust settings on the device.
Again fwiw, both of my parents now have iPads and use them daily without buggering them up too badly. Every once in a while I get over to visit them to address any issues. Basically patience is your best friend regardless of what platform you choose.