I would suggest that you set aside a certain time three days a week that is school time for thirty minutes. Call a meeting of all the kids and let them decide on the time -- majority rules. No matter what, do your best not to deviate from that time.
During that thirty minutes you need to do a song and dance act -- you need to capture all of their attention. Read to them with great theatrics. Get lots of simple books and read four or five with great expression and then pass them out and have three of the kids read to the other three (next time reverse it). You will have modeled great reading and they will have just heard the vocabulary. You be there to verify they are doing a good job and pass out the praise. End the session by reading one chapter from a book that will hold all of their interest, like The BFG by Roald Dahl.
You want to make that half hour enjoyable and captivating. The children who have issues with attention will be able to attend to the task at hand if you capture their interest. Don't worry if they fidget or have their bodies spread all over the floor. Don't allow any food, TV, or video. Once you have them hooked, you can start throwing in a few mental math problems where they have to figure out problems in their head. The important thing is to create a positive attitude toward learning, particularly reading, and to establish good work habits which begin with being on time and having the proper attitude.
The local public library is the best place to get a list of specific books and software. The children's librarian will know what the most popular books are for children in your area. If that isn't possible, elsewhere on this site you can "Ask the Researcher" and a list can be provided for you.