Sorry for replying to my own post before getting a response, but I noticed I'm going to have a similar issue buying the expansion packs for PC.
When I try to buy one of the expansion packs for PC, I choose "EA App for Windows". This asks me to login to my EA account. I can't login as my daughter's underage account because I have to use an account with an e-mail address - her underage account only has an EA ID that is associated with my e-mail address. Logging in with just the EA ID is supported in the EA App but not on the website when buying games. So I can't buy the game for her directly - looks like I'd have to buy it as me and then reach out to EA Support and ask them if they could transfer it just like I need to do with the base game.
I was hoping that when I bought it I would be provided a code that I could then use when she logs in to her underage account using the EA App (as redeeming codes is about the only thing underage accounts can do, it seems). But that doesn't seem possible. Googling "buying sims 4 expansion packs as gifts" returns a bunch of links that make references to Origin gifting options and wishlists that don't appear to exist anymore. Clicking on links in those instructions just takes you back to EA's website.
So if I want to buy expansion packs for my daughter's underage account, is my only option to do it through brick and mortar stores or online places like Amazon where I will presumably get a code? Or is there a way to do it through EA that I'm missing? EA has some great sales on expansion packs that I'd love to take advantage of, but I see no way of getting those purchases to my daughter's underage account.
Thanks again in advance for any help or advice anyone can offer...