Fan-bloody-tastic. Anything for ka-ching I guess, bloody rip off.

Well, can't fault you for not knowing, but after a year a "chapter" will become a regular DLC included in ESO+. Classes originally included then become a separate purchase while the price tag of the DLC drops a little compared to the chapter purchase. Note that preordering the game and its newest chapter also includes all previous chapter DLC.
So if you want to give your child Greymoor, Blackwood and High Isle at some point, I would recommend you preorder next year's chapter (not as an upgrade but as the full game, which can then be used like a regular upgrade code - except that it costs like 10$ more but includes the previous chapters and the upgrade doesn't). Doing it that way saves you quite a bit of money, if you were planning on getting all of these former chapters at some point. There are also new DLC megabundles that include some of these former chapter DLCs alongside the other associated DLC, which can also save you some money if you don't opt for the other method.

Also do look into ESO+ as you get immediate access to all DLC with that except for the current chapter zone, but you also get 1650 crowns per month to spend on things such as classes. With a month of ESO+ you could for example unlock jewelry crafting, the psijic skill line, Thieves Guild and Dark Brotherhood skill lines, antiquities and Blackwood's two companions and you'd still have the 1650 crowns left - all of which you get to keep even after your subscription expires. Provided you did unlock it during that time, which is a lot to ask for in just one month.

There is a ton of stuff to buy in ESO and it probably is confusing on purpose, but there are ways out there to save a lot of money.