No learning will take place if you cannot get and retain their attention. You already know how hard that is. If they are verbal, to get their attention, say their name and make sure they are looking at you or at what it is that you want them to focus on. For example, “Johnny, point your eyes at me!” or “Johnny, point your eyes at the tooth brush!”
If they do not have language, or if you are going to need picture schedules or instructions, say “Ricky, point your eyes at your schedule, it is time to brush teeth”. Details on why and how to use schedules are below.
If you start talking to them and they are not looking at you, even if there are only two of you in the whole house, they will not assume that you are talking to them. They talk to no one in particular all the time. Why would they think that you do things differently? All of us assume that other people learn like we do or pay attention to things that we pay attention to – until experience teaches us that it is not the case.