If you want to organize an integrated event, it's important to brief the other adults and remind them that what they're doing should be accessible to anyone. For instance, "This does not have to be tailored to kids, but you should feel empowered to invite kids in and answer questions" Have lots of tactile stuff for kids to play with. If you're expecting very young kids, bring a set of large / indestructible things that are just for them so they can play freely without worrying about them choking or breaking stuff. Create permeable boundaries for projects and activities. Make things as hands-on as possible. Always have drawing materials on hand. Be willing to talk to kids in the same way you're willing to talk to adults.
Kids have shorter attention spans, so it's important to think of ways to invite them into what you're doing (which they are typically pretty curious about) while also making it OK for them to leave when they get bored. For an integrated event, you don't need to dumb it down or tailor it specifically to kids -- you just need to be willing (and not worried) about engaging with them if and when they ask questions. It's also important to identify one or two people who are going to be point people for keeping an eye on the kids so that parents can more freely engage.
If you want to organize a separate space that is kid-friendly, you mostly just need to staff it and fill it with interesting things. This can be hard. A typical conference space there often doesn't provide that much for kids to do unless you bring it yourself, so that's a different question.