The way I look at the current iPad line up right now is this…
iPad - This is a perfect budget option, gives all the features of iPadOS at a more affordable price, excellent for the kids as at its price point you don’t mind scuffs and odd bits of damage to it etc…
iPad mini - If you want a tablet and will never use it as a laptop setup, this is the perfect size for most, it has everything that the iPad Air does and more with the exception of the screen size.
iPad Air - Again this perfect as a tablet but if you want to use it as a laptop setup you can easily do that also, this is a perfect two in one at a friendly price, however, it seems a bit outdated now in comparison to the rest of the line up.
iPad Pro 11 - Pretty much the iPad Air but with all the extra bells and whistles, if you want to splash a bit extra for better cameras, speakers etc… this is the way to go, again this is a perfect two in one iPad, perfect if you you will be using it as a both a tablet and laptop set up.
iPad Pro 12.9 - This is a subjective one, but this is perfect if you are primarily going to be using it with a keyboard case at a desk of some kind, it’s not the best when used in tablet mode, but great as a laptop set up… but if you are planning on using this as a laptop set up the vast majority of the time, you really need to consider an M1 MacBook… because the price of this plus a keyboard is probably going to out weigh the price of a Mac, yet a Mac can do far more real work than an iPad likely ever will.