Short advice from Ming @ Agents of Speech on encouraging speech in language-delayed children. Ming recommends parents "keep modeling what you want to hear," using one- or two-word descriptions matched to the child’s current level, and, if single words are too hard, using sound play (babbling, playful sounds) to make speech attempts more achievable.
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Keep modeling what you want to hear. I see that a lot of parents will keep on asking and prompting the child to speak. The problem with it is that speech delayed or language delayed children, to be more exact, they do not have the prowess, the ability to talk. So if you keep on repeating something without helping them to do something easier, or giving more hints or making it more achievable for him, it's going to be frustrating and they're just going to ignore you. So that's why you need to keep on modeling what kind of language you want to hear from them. And that doesn't mean that you speak in whole sentences or ask questions or give commands. What you should do is to describe in like one or two words at the level that your child is operating at right now. Maybe your child isn't speaking. Therefore, the best way to give them the correct language input or modeling is one word. And if that one word is too difficult, just try sounds. Do some sound play. If you don't know what it is, sound play is just adding weird sound and babbling.