The present progressive “-ing” grammatical marker is the one we tack on the end of a verb to say that the action is currently happening. For example, we might say “he is running” or “she is flying”.
First we need to teach your child to include the “-ing” on simple verbs. You will need a set of pictures of children or adults performing different actions.
Show your child one picture and say “what is she doing?” Your child should already know the name of the action that the person is doing. If not, go back and teach those first. Your child will probably say the action word without using the “-ing” on the end. For example, if you say “what is she doing?”, your child may say “sit”. Repeat the word back to your child but add the “- ing” to the end. You can say “Sitting. She is sitting.” Then, have your child repeat “sitting” back to you. Do the same thing for each picture. Model the correct “-ing” form of the verb for each one. As you continue to do this, your child should begin to include the “-ing” on some of them by herself. Once she can label the cards using an “-ing” ending, start asking her the same question about other pictures or real people. If you see someone at the park, ask your child “what is she doing?” and help her respond with the correct “-ing” on the end. The more places you can do this with your child, the quicker she will learn to use it and generalize it to other settings.
Now that your child knows how to use the “-ing”, let’s bump it up to saying it in sentences. Get out the action pictures you used from step one again but this time prompt your child with “tell me about this picture”. The response we are looking for now is a full sentence about what the person in the picture is doing. The first several times you do this, you will need to tell him the answer and let him repeat it back to you. He will be used to saying just the single word and it will take some practice to get the whole sentence out. If you know the name of the character or person in the picture, you can say her name when you describe what she’s doing, such as “Dora is jumping”. If not, you can say “he” or “she”. If your child is having trouble with “he” and “she”, now would be a great time to work on those as well. Just make sure you don’t lose sight of whether your child is using the “- ing” on the verb. After having your child repeat the answer back to you several times, try asking him one and see if he will give you the whole sentence on his own. If he just tells you the name of the action again, you can prompt him by saying “use all of your words” and then get him started by saying “he…” and let him finish. Eventually, he should be able to create these sentences all on his own.