That most children should be able to read when beginning kindergarten is well known by psychologists though this depends on their earlier experience. Parents should begin reading to their toddlers about the age of 2 1/2, having them sit beside them and running the parent's finger along the lines as they read. If done, most children will be able to read simple books by the time they start school.
They do this by using the same inborn cognitive mechanism that they used to learn the grammatical structure of the language of the country into which they were born. Thus a child born in Spain naturally learns to speak Spanish and a child born in France naturally learns to speak French, not by memorizing the placement of one word after the other which would be impossible, but by inducting the grammatical structure of the language. Similarly, a young child, if provided a helpful experience with reading, will induct its nature and learn to read.
No expensive gadgets are necessary for this critical childhood achievement, just simple books and willing parents. Try it.