Everything is “I I I I” and the world revolves around them. When they finally get the concept of “I” and that it is actually them they will start commenting on their actions like no other!
We find it often happens with things that “go wrong”. For instance, if something broke they may say “I broke” or if they’re falling they say “I falling”. Use any opportunity to comment on what you are doing, so they begin to understand the concept. If you are cooking, you can say “I’m cutting”, “I’m mixing”, etc.
A great way to get longer “I” statements out of them is asking questions such as “What are you doing” or “Tell me about what you’re doing” to keep it open-ended. It may lead to “I eating yogurt” or “I playing Legos” – and hopefully one day “I giving Mommy a massage!” 😉 And it doesn’t always have to be an action… you can move onto feelings or attributes such as “I sad” or “I have blue eyes”.
This will later lead to the concept of “you” as you keep talking about what you are doing at the moment and what they are doing such as “I am reading” and “You are playing”. It is also helpful to point to who you are talking about so it becomes more visual. Have fun teaching pronouns!