Three games like Diablo IV you can play with your kids!
Minecraft Dungeons
I admittedly slept on this one until my kids suggested it after seeing it in a local Gamestop. I'm not much of a Minecraft guy and our house isn't really keen on it either but something about it called to my kids. I'm glad they talked me into it because this is a fantastic action RPG you can play with your kids.
Minecraft Dungeons plays JUST like Diablo. You have a central hub world that slowly opens up with merchants and special places as you save more of the land. Controls are very similar as well. Camera view is the exact same angle as well. You couldn't get more Diablo-like.
In Minecraft Dungeons, your character(s) is/are tasked with saving the town from a tiny evil sorcerer who's raising chaos (and the occasional dead) all over the land. As is gaming tradition you have to go out and stop it before all is lost. The story isn't going to win any awards and that's honestly fine for a game like this.
One thing I really like about this game is that there are no classes what-so-ever. Instead, any character can equip any weapon. If your child gets super tired of their slow two-handed sword and wants a change of pace, it's as simple as finding a pair of daggers out in the wild with a good attack stat.
The stats are very easy to understand for kids too. If the number representing attack strength is green, it's better. If it's red it's worse. Same with the armor. Older players can also get caught up in reading further looking for special effects and bonus stats but you don't need it to survive.
There are also a lot of wacky weapons that liven up the game. For every sword, there's a fishing rod that can be cast out to draw a stunned enemy directly to you. For every lantern you can use to summon a spirit to fight alongside you, you can find a small thing of hay that can be used to summon a llama that will also protect you. There's enough variety where the gameplay loop, even if you're spamming the same stage, always keeps upbeat and different.
The other thing me and my kids really liked is that, unlike regular Minecraft, Minecraft Dungeons is fairly linear. Go here, do this, repeat. It doesn't have that open-world sandbox thing where you constantly get distracted from goals. It gives you a simple task and you must complete it. The play/reward loop is fantastic.
Minecraft Dungeons can have up to four players playing together and you can always transfer your character over so playing on your kid's account doesn't cause you to lose any progress your character has made once you, inevitably, find yourself hooked on the game.