As a lifer of gaming (with a wife with similar tastes), prior to having kids my friends and I would have the discussions about "raising our kids right on the old games". I can't claim to be some classic purist, my last 25 years of gaming has been 90%+ Halo, with other competitive shooters and hardcore racing sims, but we still own almost all of our old systems.

My oldest is 7, and my youngest almost 5, and they came into gaming in a round-about way. My sister was visiting when the oldest was 3 or 4, and asked to play "an old Sonic 3D game". So, I pulled the Dreamcast out of storage, hooked everything up, and she played for all of 15 minutes before getting bored. However, my daughter was enamored. Immediately asked to play and even knowing how janky old Sonic was, I obliged.

Honestly, the rest is history. I'm not exaggerating when I say that our living room TV currently has a Dreamcast, a Gamecube, an Xbox One, PS3, PS4, and Switch hooked up to it. Both girls are huge Sonic fans, and play everything from rereleases of the Genesis games, to every brand new Sonic game that comes out, along with a whole mix of other age appropriate games (3D Marios, Animal Crossing, Smash Bros, and Mario Kart all being staples in our household).

My point in all of this is that if you expose them to the older stuff at a young age and it clicks, they'll explore the gaming landscape in their own way. I've also got an 11 year old brother that plays Fortnite with his friends every day, but also is trying to collect every single Lego game that's come out since they started the Lego Star Wars, Harry Potter, etc. series of games. Kids will like what they're going to like, but having parents that are enthusiastic about the breadth of what the medium has to offer will encourage them to dig being the modern offerings.