Audiences are part of your show, as such they have to be organized. An audience is like another character in a play.
A lot of performing problem come from a disorganized audience. All performances organize an audience in some ways. When you go to see a play, lights dim, an announcement about cell phones and a curtain rises. The audience is all focuses on one thing. A comedian comes out, pauses...says, how's everyone doing tonight...as if I care. A circus ringmaster blows a whistle, the circus starts.
Clowns tend to be in more casual arenas, someone's living room, a classroom, a park. these are not performing areas, so it's incumbent upon us to really train an audience.
With children, part of the organization is often teaching children how to be an audience. We can have them clap their hands in unison, do a simon says sort of game or shake body parts. This focuses the kids and hopefully while you are doing one of these "games" they will learn when to talk out and when not to. You can even go over audience rules with children. I think we can be more clever than that and do rules in a fun way.
If you do a clever warm up, you can also return to it when you need. I like the body shaking (shake your hands, shake your face etc). When the kids are losing attention or get distracted by an airplane, there is a distracting child. They already know about the shaking from the beginning, I just return to it, it's an instant organization tool.