YOUR KIDS ARE SPOILED BRATS!!! haha j/k, for reference, my 2.5 year old son has figured out ios (my iphone 4s/wifes iphone 4), my asus tab, my father in-laws kindle fire & my fathers ipad. I don't think you're kids will have that hard of a time with the switch.
That said, there are a few more apps available on ios. The big one I've noticed is the Disney kids app. My son can dial in and watch a few episodes of Jake/Micky, etc on my iphone via the app. On Android, I have to take him to the website and launch the videos from there. Not a huge deal in the grand scheme of life, but now you know.
There are plenty of games on Android, but I can't really say how many vs ios are educational. Also note, I don't think the in-game purchases in Android require a password so your children may add to the credit card bill at the end of the month.. (ask me how I know)