Disable speaker on iPad - force kids to use headphones

My kids are frequently watching shows or playing games on their iPads at the same time and in the same room as us - it is a bit maddening to listen to. We have tried to get them to use the headphones we got for them, but they quickly quit using them and it is a hassle to be on them about it. Is there a way we can disable the speaker, so that they are forced to use headphones to hear their content?