Follow their interests
If you want to communicate with your child, but see they are already involved in something, do not interrupt them. Instead, join them and use words to coincide with whatever activity they are doing. Usually, this will be in the form of narration.
So, if you see your child is playing with a doll, narrate everything they are making the doll do.
Or, if they are looking at a book, you can point to the different pictures and name what they are. If there is a character that is a mouse, say "mouse." If someone is jumping, say "jump." You can also compound the effectiveness by doing the motions yourself as well as narrating.