I'm kind of happy that Partner and I are still "the kids" to both of our families. I have cousins who have kids, but we aren't close to the cousins or the kids. We don't have kids, I don't have siblings, and her siblings don't have kids either. Her sister doesn't want any and her brother is starting the adoption process with his partner, so we might have one in the family soon, but not yet.
I think I'd have problems buying "just for the kids" in general, because I like buying people gifts, at least a little something. BTW I'm the worst person to buy for. I want very little, and I buy what I want when I want it. Every year, someone asks me what I want and I tell them "Oh, I don't care, I'm sure I'll like anything you give me!" because generally that is true. Or I ask for a unicorn. So if someone told me they were going to buy only for the kids I'd be like "Yeah, I get that, that's easier, here's what the kid(s) want", but I'd probably still buy them a present regardless of their offspring status.
A few years ago, I started including a gift membership to either the zoo, aquarium or science museum.
We're doing this for my BFF and her husband this year, they go with her brother and one of the kids she works with all the time, they used to have a memebership but gave it up to save money, so we decided to get one for them. We're looking at doing one for my friend and her kids who live out of state as well. It's an awesome gift!
I did ask my mom for a memebership to our science center for Christmas once (see above, impossible to buy for), but she didn't get why I'd want that because I'm a grown up without kids.
(because I'm a grown up I bought my own)